I played this over the weekend. A few of my experiences.
1) I didn't know how to setup my button configurations until 3 games in. So I was 0-3 before I figured this out. :(
2) There are some custom boxers out there that can KO you with 15 jabs. what the hell? You're out in 2 minutes. Obviously unrealistic, and has to be addressed by EA somehow.
3) The game just needs more fighters. I'm glad they included Jesus Chaves...but what about Trinidad, Judah, Tzyu, Calzaghe? I especially want to see Moorer in lightheavy, and Hearns in welter/middle. Not enough fighters.
4) LOTS of fun, regardless, because the game is very timing based, and any fighter can beat anybody, depending on how well they stick to their game. If Robinson or Leonard stick and move they're extremely difficult to beat. If Hagler keeps the pressure on, he's almost unstoppable. But...if you switch gameplans, and try to have Hagler outjab Delahoy, goodnight Marvelous!