I know this is a bit old now, but will say a few things anyway JIC.

If you have evaluated Classic SF2 and Modern SF4 then you may have a good point of reference for what is the same throughout the series. Many of the base mechanics all function the same. Crossups, and 2-in-1's where you cancel out of a basic strike into a super move more or less function the same in every SF game, and the game play is, of course, the classic 2D format.

Most of what sets it apart(for better or worse) is in the nuance. A lot of things like EX moves in SF4 are unique to that game or were something from SF3. There are "alpha counters" that let you reverse an attack by using some of your meter. One nice thing in Alpha is that each character has more than one super move where as in SF4 you have to choose one that goes along with the characters ultra combo. In that regard SFA2 is less complicated without feeling too much like it. I think it may have also been where we first saw chain combos for characters like Guy.

SFA2 is a good solid street fighter experience. Its definitely evolved from the SF2 games and a lot of people might even consider it one of the series' high points. There was also a SFA3 which was also very good, though a bit more over the top. I don't see why anyone that loved SF2 and SF4 wouldn't also love Alpha2. If we were talking about SF3 then that might be different.

Ok well, Street Fighter IV is very similar to Street Fighter II. The Alpha series changed a fair bit, as did the III series. Street Fighter Alpha 2 is by far the best 'Alpha' game (Alpha 3 is a terrible rush job with little to no thought put into it).

Mind you this version is basically a direct port of the Playstation version with is greatly inferior to the Saturn version, which was very close to the arcade game.

Don't let that discourage you though, the port is very competant and you can have a lot of fun with it. This was my go to version before MAME could emulate the arcade version perfectly, and now I own the original CPS2 board for my Sega Blast City Cabinet.

I'd say if you like SF2/SF4, SFA2 is worth getting just because its still a very anime inspired fast fighting game.

I like SFA 2 because you can do 2 or 3 Damages Moves (Specials) in same round.
SF 2 didn't have DMs and SF 3 and 4 you can choose what SDM (1) you can do in a round.