Well off the top of my head...
-14 additional characters
- everyone has an additional Ultra Move
- rebalanced to make everyone more even (Sagat in SFIV was god-tier and Guile sucked)
-Replay your fights. This may have been in SFIV but I know something was upgraded regarding this. Too lazy to look it up.
- All characters unlocked from the start
-Minor feature, but if you were background downloading SFIV would stop the download. SSFIVAE would actually continue the download as long as you didn't do an online match
-custom soundtracks won't work online on SFIV but they play perfectly fine on SSFIVAE. Minor feature but worth mentioning.