This was a hard choice between 2 and 3. While replaying them all, 2 surprised me a lot. 1, in retrospective, aged horribly and was a real chore to get through since the difficulty is so extremely unbalanced and the checkpoints are sometimes a real mess. 2 in comparison was a gigantic step up but in the end, 3 still is a step higher and more important cause it successfully combined what 1 introduced and what 2 tremendously improved. While 1 had a lot of open world experiments and 2 was a lot more straight and extremely cinematic, 3 took both strong aspects and was the culmination of the whole series, it was the perfect finale of a legendary trilogy and still to this day the absolute highpoint of the series.

2 was the most surprising replay for me, together with 4 but I get to that in the next one.
After playing through 1 and seeing all the flaws and how badly it aged, 2 hit like a brick. Being improved literally everywhere. Gone were the unfair and unbalanced difficulty, gone were the bad checkpoints, gone were the horrible backtracking and long passages where nothing happened. 2 was incredibly cinematic, cutscenes and story everywhere with relatively short gameplay scenes in between and it was even build in a way that let you allow to run straight past through everything into the next story scene, which later Halo titles definitely won't allow to. It felt fantastic and improved so much from the first one, it's in the same category as Uncharted 1 to Uncharted 2 for me and therefore, a worthy number 2.

In terms of being a surprise, 4 was an even bigger one, but that was on me personally and not on the game, that's why 2 is overall on a better place.
For years I had in my mind that I hated 4. That 4 had an awful campaign with a lot of bad sections which felt like multiplayer firefights just cheaply integrated into the campaign with overall pretty boring and disappointing traversal and story.
Turns out my brain was living a lie and this was actually Halo Reach. Halo 4 blew me away when I replayed it, it looked phenomenal, it was cinematic as hell with an amazing presentation and it has my favorite Cortana design. It could honestly be on any of the top 3 placements, it's really great.

Halo 3 ODST was nice, back then and now. The first thing that came after 3 and as a smaller experimental campaign, it was pretty interesting. Firefights were a fantastic new idea and it still ended (kinda) with the typical Halo Warthog race which I appreciate a lot, since this disappeared forever after ODST.

Halo 1 was a chore to play through. I was chocked when I started my complete rerun of the series and noticed that 1, as the only game in the series, aged horribly (Reach and 5 were always bad). The difficulty was sometimes really unfair as well as the checkpoints and the balance also was kinda mixed with a lot of boring backtracking. I still enjoyed it overall as the classic that started the franchise, but I definitely don't need it again, like I said, it just aged really badly.

Here it is, Halo Infinite. Very early I already knew it won't beat 3, 2 or 4, but I wasn't sure if I put it above 1 (and therefore ODST) or not, I decided to not do that. Too repetitive was the gameplay, just 1 real biome, just a handful of old enemy types and story missions mostly being in the same looking structures. This ain't it chief. Yes it has one of the best pure shooting gameplay yet and it's so fun to play, but that doesn't make up for all the other flaws. Heck, even the pure open world gameplay isn't that great with a map mostly not made for cars at all and one simple grappleshot that feels limited very fast with the feeling that you should get so many more gadgets that help you to traverse in a cool way, but they never come, it never changes.
After all this time, after all the waiting, that isn't was I was hoping for. The actual story was well told and I liked it, I give it that and that makes it definitely better than 5, but I can't go any higher.

All in all, disappointing.

Halo 5. What can I say about 5. I played through it in 2017 and I played through it again this year and I already forgot most of it. The marketing campaign was a big lie, Cortana's design change and her story path is crap, the story overall is forgettable and it's just not really good. The only one I dislike more is Reach.

Halo Reach is on the bottom of my list cause I absolutely can't stand it. The campaign progression balance is just bad, many passages feel like firefight without other players and a lot of multiplayer maps were just straight ripped out of the campaign, or the campaign reused maps made for the multiplayer, either way, I really hated this back then. I really, really don't like this one. 5 was forgettable and sad, but this one was just bad.