Played a bit more, started career mode, which begins as a junior tournament, and now I've begun climbing the ranks. There's a lot more variety to the training minigames in between fights which is nice, but I failed two of them horribly outright. I'm pretty sure you can play these outside of career mode on their own, so I'd suggest doing that before jumping in to career mode to try and get a feel for them so you're not losing precious stats.
After that I started chasing the "Beat Ali on GOAT (Greatest of All Time) difficulty", which is pretty tough if you play an offensive style. It really favours countering more than anything, and heavy punches are almost useless as the AI counters them frequently.
So far my biggest dislike is how you get your boxer up off the mat when knocked down. You have to keep a marker centered on screen with the left stick while pushing up on the right. This gets harder to do the more often you get knocked down. I personally prefer the old-school way of just hitting the buttons as fast as you can, but time will tell. It's only been an issue in the "GOAT" difficulty so far, because nobody has managed to knock me down yet in career mode, but I'm sure that will change as I progress.