Oh it's massively subjective. There are lots of people who'd disagree. Too many, almost! Fandom always sides with the old stuff.
I'm not convinced they've yet recorded a truly weak song, though. I mean, there are people who'd criticise their new stuff, as there are in any fandom - but even by the standards of 'orrible people on the internet, they're not exactly struggling, nowadays. Commercially they're doing better than they ever have, and they've not done anything truly horrific - and the people who insist that they have, tend to disagree on exactly which aspects.
Even the most ardent haters of Systematic Chaos, which is, online, their most maligned album by a fairly long chalk - and those haters are magnified, in such a small and psychotic fanbase (which I fully subscribe to, by the way!) can quite often at least find a few songs they love on it. And there are only eight of the buggers, so "a few" generally encompasses at least a quarter of the album!
How many bands, at the age of 25, can say they've not only not yet dropped the ball in a big way, but they're even amassing fans at a fairly alarming rate?
How many bands, at the age of 25, can still pump out classics that make it to the top five in the "favourite song" polls? Even among the least brown-nosey fans, The Count of Tuscany's frequently considered one of their best, and I've yet to find many a-person with a bad word to say about Wither.
How many bands, at the age of 25, can have a founding member leave, and still have their fans completely optimistic, and even psyched about what's still to come?
By any barometer you can possibly think of - commercial success, album popularity, number of beloved songs - bar the on notoriously subjective "personal taste" meter, you can happily say that Dream Theater are doing ruddy well nowadays. Long may they prosper.