It's pretty hard to make a game that feels consistent while shifting between viewpoints like that. If it's not carried out perfectly, it will be a detriment to the game. It will also require a lot more artwork, even if it would be a "fake" 3D environment technique, like for instance
ray casting (most well known example: Wolfenstein 3D).
I'd say it's probably best to settle for one technique and stick with it. At least for a first game. Who knows, maybe we'll have so much fun we can make a sequel.
