Generally, to me it's a couple of different things to look out for. In multi-driver designes, you generally have to sit a certain distance from them in order for the drivers to all blend and give a cohesive sound. If you can't sit far enough away from them, your room is too small.
2nd, bass and placement. Many times, it is only possible to get good (non-bloated) bass with the speakers quite a bit away from the rear and side walls. If you don't have room to position the speakers properly, the room is too small.
3rd, some speakers don't play well at low levels, they need to be goosed with a bit of power before the "wake up". If that's the case, and you are in a small room, you may be having to play them too loud for comfort in order to get the best performance from them.