The Top Tier of Mega Man games.
It begins right after the first Zero game ends, where Zero begins his search for X, who's whereabouts are unknown. It's not long before he becomes stranded in the desert and gets rescued by the military from the first game. Events pan out and Zero meets up with Ciel once again as she explains the new crisis concerning the ancient Dark elf. So its up to him to journey through different sections of the world, via Mega Man hub world sty1e, and stop this menace. But can he trust this new leader of the military, Elpizo? Zero has no choice as the world needs him once again.
Zero has a new array of weapons to help him on his quest. The shield boomerang takes long to charge, but is very powerful for short ranged use and can reflect enemy fire; while the grappling spear can cling to ceilings and rip off enemy shields. Each weapon can be selected as either main or sub weapon, and using these weapons strategically in certain stages helps you overcome tough obstacles. And as always, the Z-saber is as proficient and fun to use as ever.
You'll need these weapons for the extremely tricky bosses that lay ahead at the end of each stage. Their attack patterns are very strict and its very easy for beginners to fail multiple times. But for those that triumph will receive the bosses' elemental attribute, which will add you on the next boss fight. Experienced players can even gain new abilities and different suits if they reach a certain overall score at the end of the stage.
And then there are the secret elves. These "elves" can be found by doing various tasks, keeping people company, and/or exploring secret areas in stages. Every elf provides a different power once per stage from giving you extra health, to saving you from pits, to destroying all surrounding enemies, etc. Elves can even level up and provide new abilities, but no matter what you do you can only use one them once for they die after use.
Its no doubt that Mega Man Zero 2 is a hard game, and that's proven by the game's clever level design. Only at rare times is it ever unfair, such is that enemies are put at cheap places and that one ledge you need to get over to is waaaaaay over there. Luckily, a lot of the tough stages have alternative routes, which may seem harder to get to, but will help you out in the long run. Ultimately, the various stage designs and secret elves to find will always make you want to come back.
Mega Man Zero 2 is action packed and fun, and its plot line is an interesting escape from the old days of "Sigma is back!" that every single X sequel regurgitated. If you like the Mega Man games, and your favorite X character is Zero, this game and the whole Zero series is a must play.