I've not read much of this thread yet (to see what others have said), but I'm in agreement with the quota that appreciates the Dream Theater wheelhouse, and likes having them as a solid, dependable band, for outputting quality, after quality release (if not, ostensibly, taking huge departures in territory explored)...they are eclectic enough, that different inflections of similar terrain, are still excellent enough, for me, as a consumer, and, ultimately, I'm all for artists doing what they choose to (and if it interests me I'll follow it/take from it what I enjoy and appreciate about it).
Having said that, however, with a big, established, heavy-weight band, such as Dream Theater, it can go the other way, and experimenting and risks are undertaken less, to- consciously, or otherwise- maintain their success- and income- from keeping close to a formula that has been/will likely be positively received by it's fanbase, at large (rather than taking a chance on significant deviations)...
Personally, I'd like a band to be honest to what they'd like to do, first and foremost- and that can include balancing personal interest, vs tailoring towards what fans might want/be successful), and, probably to be bold and experimental, and diverse, to really stimulate me (with longevity, as their own source/entity).
Dream Theater, as I've said, have a fairly high level of diversity, within quite a fixed, signature sound stream, that staying quite close to that, release to release, is usually adequate enough for me (and I did feel a fairly significant, postive evolution of sound, in their last, self-titled release, finding it warmer, and smoother, and somehow endearingly enriched).
That, being said, purely on a personal, consumer level, I'd probably embrace seeing them diversify more, and try bolder direction departures, more loyal to unbridled artistry, and creative freedom, than otherwise (but this is conflicted, for me, somewhat, at this point, too, against the identity/legacy of such a mainstay, big band- do you want to mess with that too much/pull a wider breadth into it, or should you keep it more rigid, and use other outlets for greater experimentalism?).
I think a stronger balance, in terms of experimental departures, for this outfit, can be found, however, whilst stll keeping a core grounding in Dream Theater's identity, and so, yeah, I'd be game for some stronger departures/experimentalism!
P.s// I'm probably craving something more metal-dominant, and heavy from them, currently- seeing them live for the first time, in Feburary, I was so impressed by how satisfyingly heavy their live sound was! Awesome.
P.s.2// I've not reached a point of accute, conscious analysation of Dream Theater with Portnoy, and Dream Theater with Mangini, but my naturally attained impression is of liking Mangini- as an individual musician, as a fit in the band, and as a person/personality- and I think he's blended in organically, giving a different flavour that I like.