The Imperial Army (ATAT/ATST crew) already had three uniforms, they didn't need another. Why not just reuse the ATST or ATAT uniforms?
The shoretroopers seemed very superfluous as Imperial special forces when Deathtroopers were already in the film-besides they didn't seem terribly special in their combat abilities or fighting style, and didn't seem to be amphibious assault soldiers despite what their name would imply. They could have replaced them with Imperial Navy troopers and it wouldn't have mattered.
The AT ACTs were really silly. Me and my friends speculated from the trailers that they were being used to transport materials for the construction of the death star, which rebels were attacking to sabotage the construction of the death star. But they were just kinda....there. Popping up out of nowhere and then evaporating in seconds as soon as the rebel air force arrived. It was just bizarre and their poor combat performance makes their cousins the AT AT look less intimidating by hindsight-like the rebel base on Hoth could have been saved if they had just peeled off a X-wing or two to take out the Imperial assault force. ATSTs probably should have been used instead.
Capital Ships are made out of paper in this movie. Three Y-Wings knocked out one star destroyer, and I'm pretty sure I saw an X-wing drill a hole through the command tower of the other one at one point as well. On the Rebel side, aside from the Hammerhead, none of them really seemed to do anything except explode.
It was neat to see nods to the EU like the Juggernaut or the Hammerhead. It would have been nice to see some old clone wars tech in the rebel fleet or perhaps some Z-95s.
No Kyle Katarn.