My definition of an ideal room is one that is tuned to be musical while being relatively flat and having a nice balance of ambiance and absorption. It still maintains the characteristics of a natural space.
Some nice rooms I have been in all seem to incorporate a ton of wood (floors, cielings). haha
I agree. IMO, an ideal room has, above all, dimensions promoting a good modal distribution. This keeps the need for bass traps a bit lower, so maintaining energy is a bit easier. I think the easiest way to come with a "comfortable" working room that delivers good results is to even the decay times from low to high frequencies as much as possible, prevent simple anomalies like flutter echo, and provide good returns of late reflections through diffusion.
As the poster above has suggested - designs with a lot of wood are common. This is mostly for looks, as wood looks much better than drywall, but behind the wood is what is important as well (usually, thick porous absorption). Symmetry is a must in most rooms. I would opt for a good amount of diffusion if the space was big enough. Honestly, it really depends. Good results can be had in less than superb rooms and bad results can be had from relatively 'good' dimensions. Treatment is used/designed/purposed for specific uses in rooms to combat certain things. A more isolated space will usually require different treatments than one where isolation isn't built in.
IOW, I think the question is not really a great question in the first place. Its similar to asking what makes a great record - there are many ways to get there, many reasons that musicians and engineers made the choices and decisions for the albums, etc - but it all ends up with a great finished product. I might not enjoy the distortion on the guitar as much as another album, but that doesn't make the finished product less great. There are many purpose built rooms that sound wildly different from each other, but all great in their own respects and for their own uses. A lot of it is also personal too as you can see with things like studio monitors. Some people swear by monitors that others hate, some people spend tons of money on things that others claim give little benefit.. Whatever works for you I say!!
I think it is more important to give general rule of thumbs that are helpful to all people. Addressing harmful reflections, providing necessary bass trapping, and controlling the ambiance and decay times in a room is, most importantly, something we can ALL focus on and put some work into for the betterment of our own studios, theaters, living rooms, what have you..
