
That's something I kinda take for granted with DT albums actually, they're normally a very "full" experience as opposed to just a collection of songs chucked on a CD to comprise an album. There's always variety and contrast, it seems like they really think about the "flow"of the album, and seems like they've consistently been doing 2 parts to their albums the whole time aswell. I generally listen to albums instead of just songs because I'm normally listening for long periods of time while doing other things, but there aren't too many bands where I can do the whole album experience (and enjoy all of it) because even with some of my top bands, they still have a bunch of filler or just samey songs where only a few of them will click with me. I don't wanna sound like I'm putting DT on a pedestal because there are some really well constructed albums out there but it's nice DT do care about the bigger picture regarding this sorta thing. (pun completely intended
) You get more replay value out of the album and even some of the songs that you might not otherwise deliberately listen to. Could even play a part in why many of us know every song the band has ever done. 
I think a good way to answer the original question would be to say:
"Saved by the epic?"
No!
But..
Saved by the variety?
HELL yes!!!
In fact I HATE it when they are referred to as JUST a prog, metal or "prog-metal" band, when I know there is so much more TO them than that!
I also think that what I have been trying to say is that while I do love the variety, i'ts one of the things that makes Dream Theater one of the greatest bands ever, there are certain things, such as the ballads and the epics that are pretty much hit and miss with me, and I'm sure there are many others who see it the same way.
In other words, for every song like "The Answer lies within" or "Along for the Ride," which I think are as good as any of their earlier ballads, there are songs like "Beneath the Surface" and "Far From Heaven" that just don't DO anything for me.
Similarly there are are songs like "A Change of Seasons" and "Octavrium" that are absolute CLASSICS as far as I'm concerned, but there are other epics, such as "The Count of Tuscany" and "Illumination Theory" that, while good,to me they're a little weak, and I just don't think they're AS good as what I KNOW the band is capable of.
The same can be said for a lot of the songs in the other categories as well. I don't know WHY I like "Lie" as an example, but don't much care for "The Mirror."
I guess it's just one of those things...
