As Dogmeat said, this piece would really benefit from more dramatic lighting.  You've got a really cool subject with nice details, but at the moment it looks flat.  This is because every part of it seems to be just about equally lit, like it has a spotlight facing directly towards it, if you know what I mean.  That can make even the coolest pics look boring, or at least not nearly as exciting as they should.

@Kazuya: It has gameplay advantages, especially with multiple floors.  Also, people who play/have played Tibia are used to it.
@Andre:  It looks like you made the smaller one by resizing that one.  Either way, the same issues exist.

It's not really isometric; it's more like isometric rotated 45% counterclockwise.  Once you get used to the look, it has the same benefits as isometric; you see the top, the side and the front of an object all in one view, and it lets you pack more detail into a small space.  It was more widely used back in "the day," most famously by a few of the Ultima games, and later by Tibia (an old mmorpg which, interestingly enough, "borrowed" its graphics from ultima IV (I think it was IV, somewhere around there) at the start).  Anyway, it's not a "real" perspective, in that you can't get it in real life, but once your brain adjusts to it it looks alright.
Anyway, @Andre: I like the head and neck on that dragon, but the rest of it really lacks detail.  The back seems to be flat noise and his wings are pasted flat against his body.  Think a bit about how he's put together.  His back shouldn't just be flat; it's going to have muscles and a spine.  The wings need to be moved back a bit (where do they connect to his body?) and they would probably look better if they were spread out.  His legs, feet and tail also seem to lack detail; they look more like tubes than actual features.

Hellboy, I take it?
Beyond what Tocky said, I'd suggest that you make the light from the gun reflect off of his skin.  It could be nice as a secondary light source for his face.

It... doesn't look much like a leopard.  At all.

That's a leopard.
What you have there doesn't really look feline at all.  I don't mean to be harsh, but you need to use reference for the anatomy.