Dream Theater has seven songs that are more often than not considered epics with five that are almost always considered epics. For the sake of the discussion we'll go with the seven songs (I'm in the five camp personally). Those songs would be in chronological order: A Mind Beside Itself, A Change of Seasons, Six Degrees of Inner Turbulence, Octavarium, In the Presence of Enemies, The Count of Tuscany, and Illumination Theory. Of those, only ACoS isn't on an album. So I'm gonna go album by album and analyze wether or not they were "saved by the epic" (in my opinion of course).
A Mind Beside Itself (Awake)- This album took awhile to grow on me with AMBI being one of the last songs to click. Awake is a very consistent album meaning that no one song really shines above or stinks up the joint. All of the songs are in the good to great range. This album wasn't saved by the epic because the epic isn't better than the rest. It's just as awesome.
Six Degrees of Inner Turbulence (Six Degrees of Inner Turbulence)- This is a killer album from start to finish. The title track is definitely the standout track, but that's certainly no knock on the rest of the album. The Glass Prison and Blind Faith are classics as well, and Misunderstood, The Great Debate, and Disappear are only slightly below that. This album didn't have to be saved by the epic but SDoIT made the album other worldly.
Octavarium (Octavarium)- This is where many on this forum say the "saved by the epic" mentality started, but I don't think this album was. I have made it very clear on here that 8VM is my favorite DT song by a lot. The amount of thought that went into it is amazing, and the end result is one of the greatest pieces of music in history. But to say an album with The Root of All Evil, These Walls, Panic Attack, and Sacrificed Sons is only good because of one long song is ludicrous. This is another case of the epic being the clear standout on a overall fantastic album.
In The Presence of Enemies (Systematic Chaos)- This is the closest I say an album has come to being saved by the epic. This is a weaker effort than the band usually puts out, but it's still a fantastic album. With that said, ITPoE is easily the best song on it because the rest is overall just ok. Except for the fact that it isn't. This may be controversial, but Forsaken, Constant Motion, and Repentance are all great songs. Prophets of War gets way more hate than it deserves, and is actually a very enjoyable song if given a chance. The Dark Eternal Night is also a fun song. And The Ministry of Lost Souls is very close to the top tier of Dream Theater songs and has one of their best instrumental sections. The epic this time around is a little weaker. It's the best song on the disc, but to say it saved a weak album is just plain wrong.
The Count of Tuscany (Black Clouds & Silver Linings)- This album gets a ridiculous amount of hate but TCoT is generally liked. Once again the clear standout, but this album also has A Nightmare to Remember and The Shattered Fortress. Also, The Best of Times is vastly underrated and has one of John Petrucci's best solos. Wither and A Rite of Passage are good songs as well, although nowhere near the quality of the four long songs. But with four great and long songs, this album isn't only saved by the longest of the bunch.
Time for some controversy.
Illumination Theory (Dream Theater)- A big part of what makes these long songs so great is that they usually close the album and offer a great ending to a great group of songs. Learning to Live, Trial of Tears, Six Degrees of Inner Turbulence, In the Name of God, Octavarium, In The Presence of Enemies Pt. 2, The Count of Tuscany, and Illumination Theory are all the longest and last song on their album. With the self titled album, you have eight short songs that are all about the same quality with Surrender to Reason probably being the best of those. The last song is the 22 minute and 17 second (19:15 if you don't count the easter egg) Illumination Theory. The big payoff. But it leaves a lot to be desired. In this case, the epic actually brings the album down, because the climax and resolution to the collective journey that is the album isn't as strong this time. The album feels incomplete because it didn't end well. Illumination Theory is a good song, but not strong enough to enhance a generally decent album and brings it down to ok level.
Overall, Dream Theater has never relied on their long song to make their album good. They just are really good at writing music. They don't have a bad song. With so much quality music, quantity does start to come into play. And 20 minutes of amazing music trumps 8 minutes of amazing music any day. Also, with progressive rock, it's all about the adventure that the music goes. There's more exploration possible when a song is longer. The Count of Tuscany can go to more places than The Enemy Inside can. It doesn't mean the short songs are bad, because they're great. It's just a different writing process. In the end, I'll listen to anything Dream Theater puts out, but I look forward to the journey that their longer songs bring me on just a little more than the shorter songs. Still, it's just a small part of the overall journey that the whole album takes you on, and that's always the best 75 minutes of my life.