So, how are people doing with this game? So far I've been having a pretty easy time; I just keep my block up the entire time, wait until the CPU throws a punch, and then hit them back once or twice before putting my guard up. It's working well so far, but I'm only up to like bronze jungle, so I have a long way to go. Does it start getting tougher? Do I have to start (yech) dodging later? Does anyone actually charge their punches?
I just finished the game here, so I guess I could answer your questions.
Yes, it does get harder later on, but not to the point where you actually need to dodge. Though dodging is a bit helpful for opponents whose punches tend to charge aka take a while to go through.
Blocking helps reduce the damage you take, but not entirely. Every boxer, regardless of their strength, seems to reduce your life by one row of pixels with four or five blocked punches. Fortunately, the same can be said of theirs as well.
As for how it gets difficult, well, let's just say that some of them "punish" you for that strategy by flicking a fierce jab at you right after your jab and majority of those who use that tactic tend to be 5-stars in strength, so yeah. It doesn't help that the touch system isn't that accurate, prompting you to throw uppercuts or hooks on occasion when you just tap the screen, and the hit detection seems compromised half the time when your jab does nothing to your opponents, even though it looks like you should have hit them.
But your best bet is still blocking and generally playing defensively: even if you get knocked down before they do (and believe me, you'll get knocked down like 5-6 times in some of the harder fights), you still have chocolate bars on your side to keep your health, which pop up when you're not in the green zone anymore.
As for charging punches, I only do that when my opponent is taunting me and it's only good against some, since some taunts go way too fast for a fully charged jab.