I still get why folks are disappointed with Apocalypse. The makeup left something to be desired, and Kinberg's script (save for the nuclear weapons scene) gave him very little of interest to do. However, I do think as time has passed Oscar Isaac was quite entertaining in the role. I remember him far better than any comic book villain in the last two or three years of superhero movies. And his "soothing" voice and look of disdain at everything is fun. I might also be a sucker for Mummy type stories.
As for the beginning, I do agree if we got a sense of his power, like we saw him conquer a whole army by himself, in Ancient Egypt before he was trapped, the film would have been better. I actually think that was the original idea since the first page of the screenplay that Singer sent out on social media seemed to be talking about a battle. My guess is it was cut for budgetary reasons, but showing Apocalypse just lay waste to someone before having his victory parade which goes awry would have made the movie stronger.