I've listened to gear in alot of different spaces; the first thing to emerge is that bigger has usually been better than smaller. Even with smaller systems, they can be backed up to wall, subs (if involved) placed similarly, and the listener sitting in the proper distance. Even if the room is huge, the results can be good, and better than in the all too familiar "too-small" or problem room.
Problem rooms seem to be more common than not. My personal experience is that in homes/apartments/dwellings, 90+ percent are problem rooms. My brain has always registered the acoustic properties of the space I am in, and I have been aware of it since at least my early teens. I've walked into some spaces and immediately sensed a good balance in the acoustic environment.
I remember a fairly large living room in a high-end late 50's ranch; heavy carpet and drapes, etc. Lots of room for bass to develop. Exceptional room. The guy happened to have Mac and JBL, too, but we all dragged our gear over and it was a good room.
Plus, in larger rooms, and I have tried to expound on this before, with the vast majority of speakers that have their sweet spot/range of SPL, you can turn up the volume to where the speakers sound best, then move yourself accordingly so the SPL is where you like it. i.e. instead of the speaker averaging 85db at your 2.5 meter listening position, you can crank it a bit and have 85db at your 5.5 meter position; same measured db but generally quite a difference, as you are feeding more power into the room and the speaker may simply sound better playing with some juice into it.
When I enter a space with live music, I always inherently move to the room position where my ears and brain tell me the best sound will be. This is mostly amounts to the SPL/dynamics I want to hear, and a ratio of direct to reflected sound I prefer. I'm more of a fourth row guy, or a stool on the corner of the bar with a good shot of the band, than a balcony guy.
OTOH, if I can't find a spot in a club where it isn't too loud, I just leave.
Back to home audio. Spaces I have found exceptional sound over the years (and I've had systems in some pretty different places) include a large acoustically treated theater/auditorium, a church (was not echo-ey), a small den, an open basement living room, outdoors on a wood deck with boundary reinforcement.........
The common denominators included size (usually), absorption/reflection ratios, solid construction, good boundary reinforcement oppotunities, luck, and some good beer or wine. Back in the day, some rightous herb and a tar paper shack were sufficient space for the Mahavishnu Orchestra to transport one.............
Let's see some room photos of some rooms you folks believe have good sound, or some stories of good spaces and what you believe made them good.