I'm afraid I can't see the guy's point. At the end of the day, he doesn't like Dream Theater. That's about it. There's really no extended way to explain this. He just needs say "I'm not into DT," and then go listen to other music.
For example -- in an effort to turn this thing into a productive discussion which hopefully belongs on this forum -- James LaBrie's work on Octavarium and Systematic Chaos are brilliant. And I think In The Presence of Enemies (both parts taken together) is one of the most brilliant rock compositions I've ever heard. It has intelligent structure, beautiful melodies, technical brilliance -- fully applied in the service of the music, not as "wankery" -- a full range of colors, moods and tempos, and any number of other features that a musically-trained person could point to with enthusiasm. But it's also just damn good to listen to. And again, LaBrie's vocals are excellent. In the concluding segment in particular, his singing can often make my hair stand on end. There is absolutely zero to complain about, with respect to his singing on this track. (Among others -- I only use this track as an example at hand).
So again, the poster on the other site is basically using a lot of words to say "Dream Theater is not my thing." Which is fine. But the words do not really service the opinion. He used the word wankery to describe his opinion of DT's instrumentalism. Which I as a musician disagree with. But if the definition of wankery in music is to use a lot of notes to express very little, then I dare say the commenter should be careful in language not to use too many words in the same manner.
P.S. Regarding Watchtower, I think Ron Jarzombek is a Genius of Geniuses. His Blotted Science project blows my mind to smithereens every time. But I can't see what that has to do with DT.