[Phoenix Gamma]

The Zero series is a continuation of the X series, only now X disappeared and Zero needs to help humans defeat an army of X Clones that are going crazy. The gameplay is ripped right out of the original X games (so you dash, wall climb, and all that good stuff), except now Zero has the z buster, the sword, a boomerang shield, and another item that changes from game to game.

Zero doesn't get a crazy new weapon after every boss, but he gets a few elemental equips which do more damage to certain enemies and bosses. Then his weapons level up as you use them, so you get new abilities that way.

They're good games and worth checking out if you liked the SNES X series. The Japanese version is particularly interesting because it's got a shitload of blood, which is really weird to see in a Mega Man game.