Unlike the helicopters seen in Seasons 1 and 3, the one crashed on the roof was totally unrecognizable to me. Just a jumbled green CG-mess that barely looked like anything. Accuracy of equipment/weaponry shouldn't really matter though. IIRC the tank from Season 1 was a British model because they needed a hatch on the bottom, so there is precedent for going with whatever is convenient over accurate. Plus, zombie show yada yada.
Anyway, I thought the premier was pretty good. The "Big Spot" sequence was cool and I really liked what I saw of the new life at the prison. The subplot with Rick and Clara was strange; I enjoyed it, but at the same time it seemed forced and slightly out-of-place (like the bum in the cabin last season). I thought the disease was the best part though, and I am looking forward to seeing how it plays out... should be devastating for the prison group.
Lastly, was anyone surprised about the ratings for the premier? I was actually caught off-guard by the huge increase. I expected minimal or no growth after the disappointing Season 3 finale. Glad to see the show is still going strong and setting records though.