This has probably been stated on this thread before (I might have said it myself...) but
the obvious reason for disliking DT and prog metal in general is just that -
it's metal.
Yuck
DT are "the" band of the prog metal genre, and are therefore either loved or hated.
And no, I do not view Uriah Heep as prog metal, but semi-proggish hard rock...
I always feel disappointed (and sometimes even sad or angry) when I say
to ppl that I love progressive rock and they go "oh, you like Dream
Theater and Tool, too..."
well... err... NO.
To discuss the possible rip-off of Metallica riffs by DT is a waste of
time. Whether they have done it or not does not make anyone like or
dislike them - though it might cause someone to despise such an action,
and the process of despising might actually lead to disliking the
band's whole output...
Obviously, those who have never craved for a torture of their ears have never heard of metallica in the first place

(just kidding... well, at least somewhat).
Cheers
-Beau