Johnnyb53 hits most of the major points concerning omnis and dipoles. I would add that all speakers bring the room into the mix; omnis make it more obvious. In most ordinary rooms, all speakers do better with a little more 'breathing room' to reduce and delay first reflections.
This weekend I installed a pair of omnidirectional speakers in a loft style apartment—a very difficult room—brick and glass on two walls (front and right), drywall (rear and left), hardwood over concrete floor. Added to this is an asymmetry, wall to the right, open to the left. Fortunately, a high 14' ceiling of open wood joists. The room doesn't sound particularly live, but when playing full orchestra at a good volume, it overwhelmed and started sounding blocked up, although, all other genre sounded great. In this case, pulling the speakers out from the front wall hardly made a difference. Taking some measurements confirmed what I was hearing, so I compensated a little for the asymmetry by adjusting balance, and pulled back the mid & upper bass a couple dB. Still, that room needs more stuff here and there and on the walls for some absorption/diffusion to help tame the room.
This weekend I installed a pair of omnidirectional speakers in a loft style apartment—a very difficult room—brick and glass on two walls (front and right), drywall (rear and left), hardwood over concrete floor. Added to this is an asymmetry, wall to the right, open to the left. Fortunately, a high 14' ceiling of open wood joists. The room doesn't sound particularly live, but when playing full orchestra at a good volume, it overwhelmed and started sounding blocked up, although, all other genre sounded great. In this case, pulling the speakers out from the front wall hardly made a difference. Taking some measurements confirmed what I was hearing, so I compensated a little for the asymmetry by adjusting balance, and pulled back the mid & upper bass a couple dB. Still, that room needs more stuff here and there and on the walls for some absorption/diffusion to help tame the room.