I really liked the production on The Silvery Image. The drums sounded like they were recorded in a huuuuge open hall or something. Had a really great sound. Nothing really stood out on the other two albums though, production-wise.
I'm a huge fan of Steven Wilson and Devin Townsend's production work though, they're brilliant. Devin's got that wall of sound thing down pat and I couldn't imagine a world without it now. Very powerful.
Steven Wilson just has an ear for music in general, I saw a video interview of him saying he doesn't even care for music theory and time signatures and all that, he just fucks around until he finds something that sounds good, and it always works for him. He's just got that natural ability to make the music really shine.
I find the comments on the drums on "The Silvery Image" to be quite interesting. Your guess that the drums were recorded in a huge open hall couldn't be more off!

It's awesome to know someone thinks that, but I won't give away the secret to getting that drum sound just yet!
TSI was a well-balanced album mix-wise, but I don't care for the sounds we got on the instruments. The vocals were recorded through a small diaphragm condenser (that's like taking out the engine of your car and replacing it with a hamster wheel), so they were so tiny sounding. My favorite drum sound is on "A Great Divide," since that was the only one that only had samples on the snare and kick.
I'm still on a quest for the perfect guitar tone, and TSI was the first step in the right direction. I didn't get my Mesa 2:90 yet, so I was running my TriAxis through my dad's Carvin power amp. I feel the tone has no body and sounds very grainy. The guitar tone improved on each album, but I still haven't gotten it where I want it. The best so far is on "When Time Fades..." I used my PRS for almost all the guitar tracks (the pickups are more fluffy and airy, which helps fill out the harmonic spectrum); I even tuned it to C G D G B E (so my high strings are still at standard) for some tracks to get the lower notes better. I don't like the way my Petrucci 7-string handles distortion - it's so hard to control - so I refrained from actually having to use it on the recordings. I was forced to use it on 7-string heavy songs like
Possession, but when I could I preferred my PRS.
I recently got some of the older Ibanez Petruccis, which I prefer to the Music Mans, pickups wise. And besides, they look awesome. Too bad they didn't come in 7-string, so I will be unleashing a new 7-string for this next record.
To better answer the questions - I love Steven Wilson's productions as well. Some of my favorite sounding albums are Opeth's "Ghost Reveries" and pretty much all of the Porcupine Tree albums I've heard. I also like Meshuggah's production on their newer albums; it's just so different. They usually program their drums, but the cymbals are real and the drums are MIDI controlled. The guitars sound like no other guitar sound I've ever heard. That kind of tone wouldn't work for me, or pretty much any other band, but I would love to know how they did it.
I haven't listened to "prog" music in a while, so I will try to spin some of my older CDs to see if I can add to this list.