This game feels like an arcade game, and it should.
The graphics are beautiful but the glitches and ho-hum story make this game a letdown. While it will satisfy your 2D action game hunger, it lacks the Creepy atmosphere and enemies that metroid has, and the creativeness that games like castlevania brought to the table.
The controls can be a mess. Sometimes you really can't aim at the target you want to shoot because he will be in the background or foreground, and since the game is 2D, shooting in that direction is often awkward.
Collecting powerups and leveling are not entirely useful. You gain some stat bonuses like armor, more missiles and (rarely) more health. The only thing that really seems to make the biggest differences are health packs, and you can beat the game with very little of these.
Even through all these faults, the game is what you would expect. I just can't say that I was ever really engrossed. I've been spoiled by previous games of the same genre.