Persona 3 Reload was always going to be a subject of debate amongst fans for one simple reason; for many people, it failed to answer the question of "Which version of Persona 3 is the definitive version to play?". Short answer: barring a re-release, Persona 3 Reload will be the version to recommend moving forward to new fans of the series. Long answer: let's break down what Reload provides over other versions of the game, as well as where it lacks.
Visually speaking, this game looks great. The character models look better than ever, and the new UI gives the game a unique flair that I felt the original didn't have. Some people might argue that the visual presentation goes too far in the Persona 5 direction, undercutting the game's more sombre atmosphere. While I do get where people are coming from with this critique, I don't think it's true. The game does take some visual cues from Persona 5, but also maintains a more minimalist approach to the UI, similar to that of the original UI. Most people are going to go for this game's visual presentation over FES' and Portable's.
The soundtrack is a little more contentious. The game remixes all the songs and adds a few new ones for good measure. All the new additions have been really great, and I keep revisiting them. The remixes are hit-and-miss. I think the new Mass Destruction has worse instrumentation, particularly with the synth, which is very prominent and sounds like a frog got stuck in the song. In combat, it's less noticeable, but when I listen to it in isolation, my ear perks up when I hear that really loud synth. On the flip side, there are some remixes that I actually prefer over the original. The highlight being Changing Seasons. The added chorus adds a boppiness (for lack of a better term) to the song that the original is lacking, to the point where I can't see myself going back to it. The rest of the tracks are basically more or less equivalent to the original, where I don't have such strong feelings that I prefer one over the other. If you know anything about the original soundtrack, this is the good thing, seeing as that soundtrack is a favourite within the fan base.
The gameplay has been revamped from the original. Long over are the days of uncontrollable party members. This was one of the biggest criticisms of the original, and it would have been insane of Atlus had they kept it in. If that was the only thing they had changed up relating to the combat then most fans would be happy, but they also added two new features to spice up combat. The first one being the Shift mechanic. Think of it as a nerfed version of Persona 5 Royal's baton pass. It's a welcome addition that adds more depth to encounters without making them too easy. The same maybe can't be said about Theurgy. These are essentially character super moves that can be triggered when you meet certain criteria. These are incredibly powerful moves and can make certain encounters trivial. They are fun to use, so there is that. It's also the mechanic that replaces the fusion spell mechanic from FES and Portable. Instead of needing the personas in question in your party to perform the spell, you just need to have acquired them at some point and have them in your compendium.
One of the other much wanted changes is to Tartarus itself. Often derided as a boring slog in the original, it's been changed and updated in ways to make traversal more interesting and less frustrating. Some fans might be disappointed that it wasn't revamped more dramatically, but I can't see how they'd do so without ruining the core conceit of Tartarus. Have someone play Reload's version of Tartarus, then FES's, and you'll find out pretty quickly which version they'd rather go through.
All of this is nice and all, but to me the biggest improvement to the Social Links. Two big improvements were made. Firstly, all Social Links are now fully voiced. This does a lot to improve the overall experience. Previously great Social Links have been made even better with the new voice acting (shout-outs to the Hanged Man social links), while other less remarkable ones have been noticeably improved. The Magician Social Link is still very weird, though, and the voice acting just highlights how bizarre that whole link is. The second big improvement is the addition of Link Episodes. Previously, you weren't able to hang out with your male party members, which limited how much character development they could get. The Link Episodes completely rectify this and give the male party members some much-needed screen time. Ken and Shinji especially benefitted from this, as I always felt they were undercooked in the original release.
While these additions make for a much smoother and cohesive experience compared to FES, it does fail to address one criticism that I've had that exists in both versions. The way social links are spread out makes it so that the game will have bouts of the player doing pretty much nothing. Unless you're following a guide, they'll be long stretches of game where you can't hang out with anyone, which makes for a really annoying experience. This would be an element that gets improved in future games, but as it stands remains a relic from the game's original design that I wish they had fixed.
People might opine that the lack of the playable in The Answer and the absence of the FeMC make it so that we still don't have a definitive version, I think focusing in on these elements misses the forest for the trees. Reload, as of writing this, is the way to go in terms of which version to recommend to new players. You might have your preference of version, but trying to convince someone to play FES or Portable when they have a polished, beautiful looking version of the game in Reload right in front of them, you're fighting a losing battle.
Visually speaking, this game looks great. The character models look better than ever, and the new UI gives the game a unique flair that I felt the original didn't have. Some people might argue that the visual presentation goes too far in the Persona 5 direction, undercutting the game's more sombre atmosphere. While I do get where people are coming from with this critique, I don't think it's true. The game does take some visual cues from Persona 5, but also maintains a more minimalist approach to the UI, similar to that of the original UI. Most people are going to go for this game's visual presentation over FES' and Portable's.
The soundtrack is a little more contentious. The game remixes all the songs and adds a few new ones for good measure. All the new additions have been really great, and I keep revisiting them. The remixes are hit-and-miss. I think the new Mass Destruction has worse instrumentation, particularly with the synth, which is very prominent and sounds like a frog got stuck in the song. In combat, it's less noticeable, but when I listen to it in isolation, my ear perks up when I hear that really loud synth. On the flip side, there are some remixes that I actually prefer over the original. The highlight being Changing Seasons. The added chorus adds a boppiness (for lack of a better term) to the song that the original is lacking, to the point where I can't see myself going back to it. The rest of the tracks are basically more or less equivalent to the original, where I don't have such strong feelings that I prefer one over the other. If you know anything about the original soundtrack, this is the good thing, seeing as that soundtrack is a favourite within the fan base.
The gameplay has been revamped from the original. Long over are the days of uncontrollable party members. This was one of the biggest criticisms of the original, and it would have been insane of Atlus had they kept it in. If that was the only thing they had changed up relating to the combat then most fans would be happy, but they also added two new features to spice up combat. The first one being the Shift mechanic. Think of it as a nerfed version of Persona 5 Royal's baton pass. It's a welcome addition that adds more depth to encounters without making them too easy. The same maybe can't be said about Theurgy. These are essentially character super moves that can be triggered when you meet certain criteria. These are incredibly powerful moves and can make certain encounters trivial. They are fun to use, so there is that. It's also the mechanic that replaces the fusion spell mechanic from FES and Portable. Instead of needing the personas in question in your party to perform the spell, you just need to have acquired them at some point and have them in your compendium.
One of the other much wanted changes is to Tartarus itself. Often derided as a boring slog in the original, it's been changed and updated in ways to make traversal more interesting and less frustrating. Some fans might be disappointed that it wasn't revamped more dramatically, but I can't see how they'd do so without ruining the core conceit of Tartarus. Have someone play Reload's version of Tartarus, then FES's, and you'll find out pretty quickly which version they'd rather go through.
All of this is nice and all, but to me the biggest improvement to the Social Links. Two big improvements were made. Firstly, all Social Links are now fully voiced. This does a lot to improve the overall experience. Previously great Social Links have been made even better with the new voice acting (shout-outs to the Hanged Man social links), while other less remarkable ones have been noticeably improved. The Magician Social Link is still very weird, though, and the voice acting just highlights how bizarre that whole link is. The second big improvement is the addition of Link Episodes. Previously, you weren't able to hang out with your male party members, which limited how much character development they could get. The Link Episodes completely rectify this and give the male party members some much-needed screen time. Ken and Shinji especially benefitted from this, as I always felt they were undercooked in the original release.
While these additions make for a much smoother and cohesive experience compared to FES, it does fail to address one criticism that I've had that exists in both versions. The way social links are spread out makes it so that the game will have bouts of the player doing pretty much nothing. Unless you're following a guide, they'll be long stretches of game where you can't hang out with anyone, which makes for a really annoying experience. This would be an element that gets improved in future games, but as it stands remains a relic from the game's original design that I wish they had fixed.
People might opine that the lack of the playable in The Answer and the absence of the FeMC make it so that we still don't have a definitive version, I think focusing in on these elements misses the forest for the trees. Reload, as of writing this, is the way to go in terms of which version to recommend to new players. You might have your preference of version, but trying to convince someone to play FES or Portable when they have a polished, beautiful looking version of the game in Reload right in front of them, you're fighting a losing battle.