Let's start with his 'bot mode since that's the mode he was packaged in.
This is a medium range shot. This a good mode to package Grimlock in as he's quite impressive in this mode. Grimlock is a barrel chested killing machine and pretty imposing. He features a decent amount of articulation. His knees bend and twist and his elbows feature the same points of articulation.
Grimlock comes with two accessories - a shield and the ubiquitous sword. The shield pegs into either of his forearms and looks rather nice. While the sword looks great, I'm kind of over the Dinobot/sword connection. I like the double barrel blaster of the G1/Masterpiece Grimlock and would like to see that in use again.
I haven't played War For Cybertron or it's sequel Fall of Cybertron, so I don't know how accurate the figure is compared to the game, but I'm really impressed so far.
T-Rex mode is where this Grimlock loses points with me. For some reason, maybe because of the L.E.D. wiring in the head, Grimlock is very hollow, as I mentioned earlier. This leads to some issues when posing him in T-Rex mode.
I don't know why I decided to look at the instructions. When I opened them up, they just said "Do you own a Grimlock? Any Grimlock in the 29 years that Transformers has been around? Then you know how to transform this guy." Yeah, his transformation is pretty much like any other Grimlock ever released. Which is nice. Then again, maybe some new innovation in the transformation would be nice.
Size-wise, Grimlock is a good size. Not as big as the Masterpiece, but bigger than the G1 version and certainly the deluxe FOC figures (obviously). As far as articulation goes, he has knees that bend, and they rotate left and right. But due to the hollow underside, I have trouble doing any great poses; his legs keep going underneath his body. Grimlock's forearms feature one point of articulation at the connection to the body. Once again, due to the L.E.D., his head does not move, which is unfortunate. Grimlock's mouth does open, when the lever on his neck is pushed back. This also activates the L.E.D.
Overall, I think that the designers, either Hasbro or TakaraTomy, made some good decisions on Grimlock's robot mode. Grimlock towers like he should, and looks bulky. I feel like maybe a different solution should have been devised so his back/T-Rex underside wasn't hollow. This would have added some nice heft and eliminated the leg problem when in T-Rex mode. Because of this, Grimlock will more than likely never leave his 'bot mode. Unless I wanna just line up a few T-Rex's. For fun.