Metal Slug X

Takes the original game and goes fucking ham. The new enemy types create new angles in which they can approach you adding a lot of versatility to the level design. The game also has new pathways and more creative use of verticality that add a lot of cool dynamics to a much diversified and more interesting roster of boss fights. I think the new vehicles and transformations aren't horribly interesting aside from the plane, but they do add more variability to levels at least.

First 3 stages was omega nostagia trip, incredible levels, creative areas, enemies, and bosses, fat boosted mechanic, but last 2 kinda generic