Unnecessarily long hitstun and 'stop having fun' moves
Let me clarify the latter. Right now I'm playing River City Ransom: Underground, and the NERDS gang members throw beakers of fire, ice, and acid when at range. If the ice beaker hits you, you're locked in an ice cube for what feels like forever but is realistically probably ten seconds. You can't mash your way out of it, it doesn't do hardly any damage, and enemies can't/won't hit you while you're frozen so it doesn't even serve the purpose of letting them get free hits. It's just there to frustrate you, especially since the other two beakers can do friendly fire but that one can't (which would actually be helpful), and it also has a really long 'active' time from when the beaker hits to when the area is safe to move through.
EDIT: Screw it, got another one from the same game. I mean I'm enjoying it, but this is a problem.
Multiple characters that are SEVERELY imbalanced
RCR:U boasts 11 playable characters; I've yet to unlock the last three and I haven't yet really played much with one of the starters (Glen the Karate Guy), but of the seven I have played, their usefulness is all over the place. Paul (the Boxer) is an absolute beast from the get-go with a fast punch and a decent grab attack, and once you unlock his punch strings there is no character better than him at annihilating entire gangs within seconds using his cross->jab->gut punch->straight haymaker to bowl a guy into a group of enemies and then using his ground punches to deal massive damage to all of the downed foes at once. Provie (the Breakdancer) is in a far, far distant second, as she has fast kicks and a decently fast knee from a clinch, but that's about it. Bruno (the Luchadore) is a lot worse than I wish he would have been. His punch animation is slow and stupid-looking, his dropkick is nearly useless, he doesn't start with any grab moves (odd for a wrestler, even a lightweight), and his normal kicks, although they are his best attack, aren't as good as Provie's. Alex and Ryan (the original duo from RCR) are really showing their washed-up age as they both just don't start with any useful abilities or combos, but they're better than Mike (the Grappler) who has extremely slow punches (although his kicks are decent) and a slow grab attack. But the worst of all is Rudy (the Wrestler) who has slow punches, slow kicks (both of which can't combo; you just throw one and no matter how much you mash you have to wait two or three seconds to attack again), weak dash attacks that knock the enemy away so there's no chance of a follow-up, and oddly no grapple moves. It is almost impossible to level the latter two up and see if they shine at all with new abilities, because you have to buy the new techniques and dying costs half your money... of which you probably only have three dollars anyway because these two are just such shit that you can't really defeat enemies. Which is disappointing, because as a wrestling fan I really wanted Rudy and Bruno to be good. At least the Little Mac/Ippo fan in me is satisfied with the handling of Paul.