The cave is a great game and it seems to be doing really really well on steam as far i noticed.
Anyway the way i would describe the game is an adventure 2d game. There's a lot more puzzling involved using the 3 characters you have compared to defeating enemies etc. There's items u can pick up, only 1 item per character, and u have to figure out how to get them, where to use em, and sometimes having to think a lot in using the 3 characters.
It doesn't really matter which 3 characters you use. The special moves they have are really just there to give little incentive for each character. But overal i think one playthrough with "your" 3 most apealing characters should be enough... well unless there's something i dont know about yet.
Anyway to answer the OP in short. Great adventure 2d game with very good humor