Grimlock is a piece of crap. I hate to say it, but he's no better than the Classics Deluxe from several years ago. In robot mode, he's a bit gappy and lacking in a full range of articulation. Conversion involves a few moves that are similar to the original, but it's somewhat difficult to turn his robot arms into T-rex legs and position them properly, oddly enough. I can't get him to not look bow-legged. Also, his entire stomach is hollow, which makes him useless to display in any position aside from his profile. And his plastic is really low-quality. (The Joes have also had a noticeable drop in plastic quality, but they've been able to work around it for the most part so it's not such a distraction.)
Oh, but his mouth lights up when you press a button!!!!1!!!!
It might seem like I'm judging him harshly, particularly by comparing him to much-loathed Classics Grimlock, but I expect a lot more from Hasbro in 2013 than I did in 2006 (?), and the teaser of Grimlock was one of the big deals in the marketing of the game. And he's my favoritest. I don't think it's fair to judge him against Masterpiece Grimlock, but it's more than fair to judge him against Animated Grimlock, which beats the tar out of this figure.
D. This figure is so bad (particularly for the price), I'm debating whether to even open Blaster and Magnus or just return them to the store.
EDIT (a couple of hours later...)
I transformed Grimlock back to robot mode, since he's useless as a T-rex. This will be the only transforming Grimlock I can't display in dino mode (not counting versions who transform into tanks or Ford Mustangs, obviously). In robot mode, he's not as bad as I initially thought. (I suspect a lot of my hatred was over the worthlessness of his dino mode.) The articulation is still a little lacking, and he kinda looks like a 2006 figure, but he's decent enough as a robot. I've got to upgrade my grade a little, but I can't give him full marks. I'll say, based on the passability of robot mode, he's more a C. I still can't recommend him at $23+.