Agreed on the fact that posters are hard.
Anyways, here's some comments/suggestions.
-The main problem here are the two renders in the back (Trips & Roode). They're far too compressed, so they don't look 'real'. When resizing renders, always drag from the corners when you make them smaller, not from the left or right (assuming you're using PS). That way the render isn't stretched/compressed.
-Personally, I like everything to face a focal point (usually the center of the piece), so the fact that the ADR render faces outwards is weird in my book (but I'm weird so take it or leave it on this one haha).
-The Barett render doesn't work (not your fault, it's the render itself). The head is just really weird, so just be more careful with render selection.
-In terms of all the renders, you need to try to get them to have similar lighting/color. For instance, ADR is much lighter than Trips or Barrett. The way to do this is to click on each individual PSD, go to Layer and add adjustment layer (brightness/contrast), play around with the brightness and contrast until the render matches the other, and then merge that adjustment layer down on whatever render you're editing (this is assuming you're using photoshop lol).
-Cutting off the bottom of the title doesn't work for me. I'd probs just dump the text at the top and move the belt up.
-Finally, the top of the logo is smeared in places as well as Barrett's leg. Just be careful with that.
Decent piece, but it could definitely use some touching up. Nice work!