Some harsh comments but anyway as a Villan...
The main problem is styles of play and also the size of squads/players. Milner's best form for Villa, came through the centre of a 2 man midfield, we played on the counter-attack, he used to buzz around the midfield, put in plenty of tackles and as soon as we won it, he'd be on the ball, using it wide, getting himself forward into good positions and breaking away on the counter-attack. He's a good passer of the ball and at times showed creativity but isn't a 'creative' player like a Silva let's say. He was at the heart of everything, his energy, commitment and also quality with the ball always meant any time we were going forward, he was the main man carrying it forward. We played on the counter, so when we broke, we had space to break in, he was great at carrying the ball forward and finding the right options. However at City, you play a game where you have the players to simply dominate teams, you need players with a quick touch, quick thought of mind and quick feet to unlock a defence, Milner just isn't that player. Or at least needs to be given time to become that sort of player.
Suddenly he's going from breaking with the ball with a 4 on 4 with 60 yards to run into, to having the role of a wide man (a role he is not good at) or a creative midfielder with 10 men behind the ball. We struggled breaking teams down last year, yet our away form was fantastic. That's because the likes of Milner suited our style, for example, check out the goal vs Blackburn away in the cup. That's the sort of player he is.
I just don't think it's going to work at City. He's not the right player, he needs to be the focal point, doing everything, defensively and offensively. At City, that just isn't going to happen.