Okay first off if you have just Street Fighter IV you are missing out on quite a lot with the extra characters, but if you don't much care about extra characters there is not much different between the two games. I would Also like to say I picked this game up for about 20 bucks new at Sam's Club.
This is the first SF game I have played since Street Fighter II Turbo and Championship Edition, and it was GREAT. I have heard a lot of bad things from others about the previous iterations of this title that I was a bit leery about getting this one. I got Street Fighter IV for free as part of promotion with my video card and loved it, but on the computer it was missing something. So when we found Super Street Fighter IV for 20 dollars for the Xbox 360 my Wife and I decided to purchase.
There isn't much to say other than the fact that the game is exactly what you would expect from an SF title. I have only played Versus so far but the selection of characters is awesome even if six of them have more or less the same moves (Ken, Ryu, Gokuen, Akuma, Sakura, and Dan) but still even given that they all play slightly differently and are great fun.
I would recommend this game for anyone with an itch to bash up some friends in one on one combat. Very fun and very worthwhile.