I like my AR10 quite a lot. It was at least 50% cheaper than a comparable M1A, and a hell of a lot lighter.
I've got an A4 Carbine model with the 16" barrel, and it shoots every bit as good as any of the wooden stock bolt guns I've got.
I've got less than $1,400 in it, with 10 magazines and a Lepould scope, while a comparable M1A was damned near $2k, and impossible to lay hands on, even over a year ago.
The other posters are right, in that it does not handle exactly like an M4, the BCG is heavier and longer (which shifts the mag well forward), and a full magazine is a lot heavier than the 5.56 version, so the balance is shifted forward quite a ways compared to an M4.
But if you can get past that (as in, realize it's not an M4, and stop treating it like one), it's a dandy rifle.
I'm very happy with my purchase.