I don't think it's one of their strongest albums, but I still like most of it and I think the approach they took after ADTOE was interesting. What I mean by that is that they played it safe with ADTOE in my opinion (which made sense, given the circumstances), then in DT12 they took some controlled risks with going for more concise songs, as far as structure at least because there are still lots of layers in terms of instrumentation.
Production-wise, the drums and in particular the snare... let's just say it's not for me.
In my mind, I have the tracks separated in tiers:
Tier 1 - Excellent
Illumination Theory
The Bigger Picture
Tier 2 - Very Good
The Enemy Inside
The Looking Glass
Tier 3 - Good
Enigma Machine
Behind The Veil
Surrender To Reason
Tier 4 - Meh
False Awakening Suite
Along For The Ride
Overall I think it's definitely in the lower half of their discography. I haven't listened to the new one yet and it will be a while before I form an opinion anyway but out of their first 13 I would put those in the Top 6:
I&W, Awake, SFAM, SDOIT, ToT, 8V
and although I'm not sure about #7, DT12 wouldn't be a strong contender so there's that. At that point it would be a die roll between FII, The Astonishing and ADTOE I think. I have WDADU the lowest by far so DT12 is somewhere in that tier with BC&SL and SC. All these albums have many things I like and some things I don't like... but mostly things I like.