I did not enjoy the first game, simply because i felt that the characters, apart from looks, where not unique.
This time around though the developers did an excellent job of keeping things fresh and diverse, i salute you!
The character roster is bigger, and now its quality not just quantity too! The new characters are very well differentiated made so in a way that you have to adapt different play styles to master each one of them. The older characters (and the new ones) were give a second ultra. This has also changed strategies for some characters completely (Bison, Sagat, Seth etc ....) and adds more depth into a characters usage. More stages were added but that does not affect gameplay and so i won't be going in-depth.
Online mode was revamped, now there is your standard ranked match and 2 non-ranked match choices, Endless Battle (winner continues and loser goes to the back of que) and Team Battle (2 teams go face to face, Winner keeps playing until defeated and the next person in the team takes over, lasts until all members of one team are defeated). The game is clearly much more diverse now (more trials too!) but still remains a competitive online environment.
I just touched on this topic because i thought other areas are pretty well covered by others.