What I would like to see:
Less keyboard solos
LaBrie/Myung more focused on songwriting
Songs that are heavy but aren't trying to make themselves so heavy. Granted, I listen to death/black metal, so I don't mind super heaviness, but DT does not work when they are trying to emulate pseudo-thrash riffs (The Glass Prison is probably the only exception to this) and work odd time signatures into them.
Focus on a heaviness similar to Pull Me Under. Metallic, meaty but at the same time its very good and catchy. And it doesn't try too hard, which can't be said for a lot of later day DT
More democratic songwriting, Petrucci and Portnoy are great songwriters, but when the writing is spread around and not left solely to them. When they have to write everything, the ideas go nowhere.
Less Muse influence, for fucks sake.