Omega Strike is nice little non-linear platforming adventure with some RPG elements. There. That's better than throwing around "metroidvania" because this game doesn't remind me of Metroid or Castlevania in the faintest manner.

Omega Strike is unique because of the ability to swap characters-- and they swap instantly. Since each dude has his own special abilities, you can swap mid jump (or mid double jump) to cross platforms while changing the projectile of your firearm. It all feels nice and smooth. And the map is pretty well designed so that backtracking is kept to a minimal and new areas become reachable organically.

If I had to do it all over again I would have started the game on the hardest setting-- because normal was way too easy if you've played any of the previously mentioned metroidstrikevania titles.