I've always been a big Street Fighter fan. When Street Fighter II was released in arcades, I spent pretty much every day at my local 7-Eleven playing it. Even though I've played pretty much every Street Fighter iteration since then (mostly on consoles, of course), however, I haven't been able to play competitively since the golden era of the original arcade release.
I've been playing Street Fighter IV for a week now, and I think it may be the best Street Fighter release to date, which is saying a lot. It's well balanced, there are no features too technical for most players to grasp/execute (yet some great new gameplay features have been added that are well balanced), it looks great, and perhaps most importantly, it has nearly flawless online play... I feel like I'm playing Street Fighter in the arcade again. When I say it's nearly flawless, I mean there is hardly any lag. Granted, finding games could be improved, as there is no instant "find-a-game-and-join" option, but that's about the only drawback I've noticed so far.
The new additions (revenge gauge/ultra combo, EX moves, EX focus) add a lot to the gameplay and help vary the matches. An EX special move, when used properly, can be much more powerful than a regular special move, for instance. It really adds a whole other level to gameplay. As an example, if you're playing as Balrog against Ryu, you can use an EX charge punch to go right through a fireball. Before, Balrog was pretty useless against fireballs, but now he can use them to get an easy shot out. Street Fighter was always strategic in its gameplay (in high level play), but now it's seriously like playing a strategy/fighting game hybrid.
For me, playing this game online is about as good as gaming gets.