They are pretty good, though I still prefer Queensrÿche. But any music that isn't pop or mainstream rock can go under your radar very easily, if you aren't paying attention to its particular genre. How many metal songs does someone who just listens to mainstream radio know, really? Don't Fear The Reaper, Stairway to Heaven, Child in Time, Nothing Else Matters, and that'll be about it (and some of those were only big hits because they were barely metal anymore). And even if someone does go out of their way to stay up to date with certain genres, you can still never follow them all, and you may suddenly discover that you really like some group that was at its peak decades ago. Happens to me all the time, most recently with The Mamas and the Papas (yes, my musical taste is all over the place ). Sometimes such a group even did have some chart success, or quite a lot of it - Queensrÿche had a pretty big hit in the early nineties with Silent Lucidity, for instance - but that doesn't mean their music is generally played very often in places where you'd hear it. Or else it's just one or two of their songs that are played often, but nothing else (as in the case of the Mamas and the Papas).

Do you like (progressive) metal in general? I don't know as much about Dream Theater or other progressive metal bands as Jens, I'm sure, but their Best Of is pretty good, and an easier way to determine if you like them in general than to buy individual albums.