I've played it for about 9 hours so far. Really enjoying it. It is definitely like Metal Slug and Monster Hunter. These are not bad things. Multiplayer is solid, and works amazingly well, and consistently, for a relative beta.
The game has a very slow, boring start. After you get through the first wave of missions they throw at you, you'll begin learning the game's nuances, and will have more options for guns, both of which totally change your experience in playing the game.
The levels are not fantastically designed, though they could be worse. They're all very modular, which makes sense because you'll be returning to them over and over for different missions, which focus on different parts of the levels.
If you like 2-D platforming shooters in the vein of Metal Slug, there's absolutely no reason to not buy this game.