1. Lots of ONLINE features - after playing with my friend I was surprised to see how nearly all of our online match replays were saved automatically in the Player Data -> Battle Log channel! That was a really nice feature, that it automatically saves like that. And you can pick the ones you can save permanently
2. It will feel like Street Fighter IV 'Plus' - Essentially, it still is Street Fighter IV, which explains the lower price tag....but all the new characters and extra features make it worth it. It was nice of Capcom to charge a bit less for it. The game is really not just DLC + SFIV because of all the stuff they crammed in.
3. Netcode - I was on Globe (2 Mbps) and my friend was on Smart bro. Got 3 bars in our match. Lag was occasionally noticeable but mostly manageable. I've yet to try more than just one other player for online play, so I can't tell yet how much of an improvement there will be.
Overall, I'm looking forward to playing a lot with this game; it feels like the definitive fighting game right now, with all the bells and whistles to make it feel like a very complete package :D
If there's only one complaint I had to give about SSF4, it's that it doesn't seem to let you save local match replays. Only online matches are saved.
Still, great game!