The fact Street Fighter IV is on the PC is already enough to make it a great fighting game. Here's what I think of it:
Sound: 90- Well, nothing unique here, but no complaints either. During the battles the background music and sfx make the (sometimes improvized) fighting arena come to life! The only huge minus is the theme song... What is THAT supposed to be???
Controls: 75- It is really hard to write about the controls in the game. Not because I don't know what to write, but because after playing a few rounds of this game your fingers hurt! This game will break your fingers if you want to play with all the special moves of the characters. I still have absolutely no idea how to perform Zangief's super and ultra combos. Many special moves require charging that cripples your character as he or she is supposed to sit on the ground so he can execute this move. Meanwhile you AI opponent can do whatever he wants (well, the AI doesn't need to press any keys). Unfortunately, this is an old problem of the series and too bad it wasn't resolved. I mean, look at games like Mortal Kombat and see how its done right! Charge moves in MK require you to press a punch or a kick, not a DIRECTION key!!! You can also see how unfair the controls system is in the challenge mode where you are required to perform impossible combos (I never got past the third level so far). Other that this major problem the controls are easy and you can move easily around the arena even with the slowest fighter.
Replayability Value: 96- Well, it is a fighting game. A good fighting game. A fighting game with different cool modes and multiplayer (not a factor for me, but I'm sure lots of people like multiplayer). The game is fun, it is also a quick game that doesn't require a lot of your time. This is one of the reasons this game should be a permanent instalment on your PC. Oh, and the characters! They are so unique and differ from each other greatly (well, maybe except Ken and Ryu who are historically almost the same). You have great characters with cool moves (some better, some harder to control) and you really will be tempted to play with all of them to unlock them all and see the absolutely stupid movies of the game (I never found any sense in Japanese cartoons).
Overall: 89- very good! The controls and some cheap move blocking/cancelling by AI opponents are thing that make the game worse than it could be. Still, if you like fighting games, or if you just want a fun game to have on your PC when you are bored and don't want to play anything serious (like, say, Civilization) this game is a good recommendation!