Keep in mind that Street Fighter has been the pioneer for 2D fighting games. Street Fighter 3 came out in '97, with its last revision (3rd Strike) in 1999. The original Guilty Gear came out in '98, and it has had at least 4 more versions of increasing quality since then, with XX Slash coming out late last year.

3rd Strike has been *that good* since 1999 (conversely, SF2 since 1994) while the other games are still striving to get to a level where they can leave it alone. Sure, games that come after it may feel fresher with more style and substance, but that's to be expected.

Street Fighter 4 (look for an appearance next year) may just blow everything else out of the water if it doesn't tank.