Ultra Street Fighter IV is the latest and (probably) last addition to the Street Fighter IV series. It features 5 new characters, new stages, new soundtrack and tons of balance changes to the roster.

A word of advice to beginner fighters: Don't buy this game unless you have an arcade stick (fighting stick) or a good gamepad. The keyboard is not meant for fighting games, even if some people CAN make it work. Being good and enjoying a fighting game takes a lot of commitment. Hundreds of hours in minimum and thousands of hours realistically speaking.

+Great gameplay. A good entry-level fighter for beginners too.
+A huge roster of varied characters.
+Good soundtrack with many iconic songs from the past.
+Active community.
+Smooth 60 FPS animation and beautiful visuals.

-Mediocre netcode. Online multiplayer is still prone to lagging and connection time-outs. This is has been patched somewhat successfully and will be further patched in the future.
-Could use a proper tutorial à la Skullgirls. There are character trials and a manual, but no real tutorial.