The artwork feels a little plane, but only because of the kind of empty background – as far as I, the non-art-expert, can tell. So, everything you put in there are ready to be good (or even better). Maybe, a door, a window, an office table, etc. might have amend this empty feeling.

The characters look nice, their anatomy and muscles look very well planed and drawn, and even the situation looks nice to me; characters having good time together. ^^

PS. I understand you might not had time or energy to take better care of the background – you already proved, in your previous artworks, that you can draw pretty nice backgrounds.