I feel like they made the career fighter suck really bad. I could be kicking the living hell out of someone and then get KO'd with one punch. I also think that your stats degrading is somewhat difficult to keep up with.
I haven't tried career mode yet, but I read on another forum that the stats lock at 30 and 50 points. So if you train one stat all the way to 30 it won't decay below 30.
Also, if you haven't figured out how to "charge" subs than you are really missing out on some easy wins.