The gameplay tweaks after Nexus are great but the game itself ends up feeling moreso tedious, even if you just decide to the Arena only (the main mode). I'd treat it more as an Arena component expansion for Nexus. Still worth playing through all the arena and maybe some training to get nice free parts to transfer to Last Raven!
I'm pretty sure this game never retailed for full price on release anyway so they were at least aware it was just an appetizer, not a full course.

EDIT: I just played Formula Front and that game does the "3rd gen Arena game" thing way better where it has an actual personality. So if you want games with arena vibes definitely go with Master of Arena and Formula Front.

everyone: Nine Breaker sucks

absolutely everyone: It's just a really terrible minigame collection, don't play it

every single old-school Armored Core fan, everyone, in any context: Nine Breaker is the worst game in the series

me: I bet it's not that bad

me:

me: hey what the fuck

The only thing stopping me from calling this objectively the worst game in the series is that I can see what happens in it, a benchmark that not all of them clear. But like. Jesus Christ.

The gimmick of Nine Breaker is that instead of having story missions at all, you have a series of Training Exercises--I.E., minigames. You might think your expectations are appropriately tempered, you're not expecting more than a minigame collection, you're emulating this because it's 2024 and you didn't buy it for full price, it can't hurt you.

What you're not realizing is that the minigames are tuned to Armored Core difficulty. Most of them set you an extremely specific task, and many of them expect you to perform it to an absurd speedrunner-level standard of perfection. This makes the game feel both incredibly boring and infuriatingly unfair.

Of course, not all of them are at peak difficulty; some will be total facerolls, and you won't know which because the game clearly doesn't know either. The exercises are separated by category and each one has five ascending difficulty levels--except sometimes by far the hardest version of an exercise happens at level 2, level 5 is sometimes the hardest but more often literally can't be failed, many groups of exercises are totally redundant... it's an incredibly half-baked game.

There's also an arena, which ostensibly has equal billing with Training--they're trying to do Master of Arena again, kind of. But even the arena is one of the least fleshed-out in the series; you don't so much fight your way up through the rankings as fight whoever you want to gain points, then certain point totals unlock the next tier of opponents.

The high-ranking arena opponents are also super obviously using OP-INTENSIFY/Human Plus, which is a series tradition except that in most games it's also possible for you to acquire those without cheating. Hell, even in the games where I never did, it never really felt as.... In-Your-Face Bullshit as some of the arena matches in this one. We're talking tank legs that spend the entire fight in the air spamming heavy energy cannons.

So, this game is not just skippable; skipping it is recommended in the strongest possible terms. Why didn't *I* skip it? Or give up when it got to be total horseshit? Well, for one, I came to it so late in the process of Playing Every Game in the Series that I was too committed to the bit to add an "except that one." The cost has NEVER been more sunk. Make no mistake: I am a dumbass. Don't play Nine Breaker.

Not even for this reason.

Alright, let's get this out of the way, this game isn't amazing. Definitely the weakest FromSoftware game I've played but there are some things I like. For one, it's the mechanics of 'Armored Core' and gen 3.5 too, so obviously the game is fun. However, this is basically an Arena or AC on AC focused title, and to it's credit it is very good at this so long as you are loading a 'Nexus' save.
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EDIT: THIS IS WRONG, apparently you'll be locked out of getting certain parts for doing this so I may have really messed up, lol.
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This is by far the most 'expansion' one of these 'expansion games' has ever been as it's basically a great Arena mode with tons of fun opponents and matchmaking preferences that is to be added onto 'Nexus', due to having no shop and leaving new saves to slowly gain new parts by progressing in it and the totally vapid tutorials 'Armored Core: Nine Breaker' which eventually roll the credits on the game. This is really what brings in down, in the sense that this just feels like 'Armored Core: Nexus' disc 3 and is weird as a standalone release. Because doing tutorials for hours to actually beat it? It's as suffocatingly boring as it sounds, but the Arena itself is good fun with the new balancing if you have a nice AC to load with you.

So yeah, I can't recommend it as essential playing, but it wasn't the worst thing I've played.

yeah ok i played one hour and dropped it, i already knew about it beforehand but this game is just "training missions" that aren't really fun to go through, and an arena that does have an interesting concept behind it at least, instead of going up by beating your opponents you win or lose points depending on if you win/lose and that's about it. There's no shop so you need to have bought everything in nexus if you want to play, i could grind the arena to get top rank and do some missions but honestly i can't be assed to do so, maybe if i thought nexus had the sickest gameplay ever it'd be cool but i don't so eh, i got better things to do

I made a promise to myself to beat every single armored core game in prep for AC6, and every single game has been good to great so far(besides formula front but that ones like fine I guess), this game, has made my blood boil, more then any other fromsoft game, and i beat pre patch radahn and melania solo. I know what people are thinking who've played this game "its not THAT hard" and youd be correct, its not, its probably not even the second hardest AC game, but it is so tedious, and boring, and overall just unfair compared to the other ones(so far). This game is about becoming a ninebreaker, except its actually not, you cant beat the game by playing the arena, in fact, you can literally not touch the arena once and beat it, this game is actually about tedious training missions that require so much time outside of the actual mission, just recustomizing your mech for a mission because you literally cant do it at all with this mech, you end up switching your entire mech kit every 10 to 15 minutes, and with the amount of parts in this game, usually i spend longer customizing then actually playing with that mech. Anyways, this game sucks, idk how you make an AC game boring and tedious, but they did it, fromsoft can make a bad game seemingly.