If anyone's going to this to finally see Unicron..you're gonna be pretty disappointed. I'd guestimate that in the entirety of the movie Unicron has maybe 2 minutes of screen time tops? The whole gimmick behind this is Unicron is stuck in a dead galaxy after having consumed so many planets, but there is a "transwarp key" (which becomes the maguffin for the movie) that Unicron has his stooges out hunting for so he can get to other galaxies and consume their planets. It reminds me a lot of dark of the moon where we had the spacebridge pillars that pull cybertron into orbit then when they get deactivated it gets pushed back. Same gimmick here essentially.
Prime in this is very distrusting of humans which changes as the movie goes on, unusual to see him without a robo-boner for humans for once.
But Unicron basically does a big zero in terms of Unicron stuff like planet munching unless I missed something, you don't see it consume anything, you see it hovering at the edge of the maximals planet as in the trailer, then you see it start to come close to earth only to get pushed back at the end. But they basically say Unicron is still out there and prime and his team will destroy him if he returns, and we round the movie off with Optimus giving his standard self masturbatory speech.
Mirage had a few good one liners that got some laughs
Overall wasn't bad, just nothing really new.