6:00 or Constant Motion are probably my least favorite Dream Theater songs that I know off the top of my head. Neither of those songs are bad but sometimes they annoy me.
But I'm not the most fit fan to judge DT material, I only have listened to six Dream Theater albums: Images And Words, Awake, Train Of Thought, Octavarium, Systematic Chaos, and Black Clouds & Silver Linings because those were the only ones the libraries near me had. On a more positive note, I did just buy Six Degrees Of Inner Turublence off iTunes and I am psyched to listen to that whenever I get a chance. Just started my first semester of my freshman year of college three days ago so it might be a couple weeks though until I get to listen to SDOIT.