The writing when Moore was still in the band was the best. Afterward portnoy and petrucci were ok for a while, then when rudess joined there were 2 solid albums, then, stale.
I would say that dream theater is my favorite band though. I also listen to a lot of guitar based music. The largest influence in my playing was Jason Becker. I spent a solid two years playing his material constantly. Now, I may have lost some of the love of his music through repetition, but my playing is extremely technically proficient 15 years later.
http://www.youtube.com/watch?v=5qCQLyb0-mI
I've seen dream theater live 3 times, great show. But, the best show I've ever seen was Steve via in a small club. He played for 3 1/2 hours of pure energy.