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Devil suit? Evil? Generic? From an art standpoint, Fallout 2's suit looks like an oversized, hunchbacked bug. Fallout 3's just looks like advanced armor. The first showing of Fallout 2's Enclave armor that most people see is the video of the Enclave soldier mercilessly shooting innocent civilians as they exit a vault with a close-up to the Enclave armor's stoic eye lenses as they flash with the reflection of gunfire. How does the Fallout 3 Enclave armor look generic or more evil?
You're associating the first depiction of the Enclave with their armor itself. The fact that the Enclave was first depicted as shooting civilians doesn't really mean that the armor itself looks evil (while I personally do think it looks a little bit more intimidating than the T-51b).
Also, the APA being bulky was consistent with the depiction of the T-51b in Fallout.
I won't really comment about genericness, since I find it's become a bit of a buzzword, but I think that the APA MkII as depicted in Fallout 3 looks a little bit less retrofuturistic. (I didn't mind the look of the Hellfire armor though.)