I downloaded A Moon Shaped Pool this morning (paid for of course) and listened to it on the way into work. It's going to take a couple of listens to get into, but overall it seems ok, if somewhat navel gazing. It's certainly not as challenging as TKOL which remains my favourite RH album by a hair.
As far as the production and mastering is concerned, IMO it has simply been mixed and mastered warm - nothing wrong with that as that's obviously the intent, but I can see where some head fi-ers might get the impression that it's less than ideal as it doesn't throw detail in your face. If it did, however, then the album wouldn't have the same atmosphere and feeling.
Nicely mastered records? Not sure, but Pablo Honey>=In Rainbows>>>More compressed Radiohead releases.
Compression as in dynamic range compression is widely misunderstood. A compressor is simply an automatic gain control which cuts the volume by a preset ratio when the signal goes above a preset threshold. There are also parameters to set how fast the compressor reacts. The truth is that without compression a lot of modern records, outside of jazz, acoustic, and classical, wouldn't be as cohesive as they are with a bit of compression. Carefully using all of the settings Compression can be used as a sound shaper, allowing for further creativity. Compression is actually a good thing in a lot of situations.
When people complain of dynamic range compression, what they are generally referring to is brickwall limiting (which admittedly is an very extreme form of compression) which is often used to make a track sound louder than it actually is, and also to ensure that the track has an approximate equivalent volume throughout. When overdone it's bad, very bad, but when applied with care it can gel a track together and make it sound complete. Again, pretty much every modern track has some limiting applied.
Compression and limiting aren't bad things in themselves, it's how they are used which can be bad.