I have only two criticisms. (Three if I echoed Joerhyno about the armor for the exposed forearm)
1) I think the Ret Trooper head is too small and pinheaded for the large body. (If you were going for the 'roided out look, then I'd call it a success)
2) Any legs that are shorter than Ret. Roadrock legs(wave 1, wave 2, etc) give the body apelike proportions.
Other than that, I think it looks good.