I'm glad he's not our coach anymore. I'm sad he's no longer OCing the Giants.
That being said, I think his coaching mediocrity is all Jerry's fault. If Garrett had been a QB coach for a lot longer under a good coach using a modern offensive system and then if he slowly transitioned to OC under that coach, he might have been really good.
Jerry promoted him way too soon and then did what Jerry always does to his coaches. Hamstrings them and keeps the Jerry culture. I think that gave Garrett bad habits and since he never really learned that his system is too outdated because of his lack of coaching experience before being promoted, he got set in his ways. That's why a lot of old coaches get fired or phased out. The game passes them by. Garrett got it early because he got set in his ways too soon.
At least that's how I look at it. And Moore is going down that same road.