Like most players, he's improved the more he's played with them, he really did have some shocking games, but most players do, and Kompany certainly has. You could make the argument that Kompany is worse when Demichelis plays because he doesn't trust him so tries to jump ahead of the game to cut out the danger, which leaves the defence open when he fails. I'm not so sure I'd buy that, maybe to some degree but Kompany has made a lot of mistakes you wouldn't expect of him. All players have their bad spells though.
I did defend him when it came to that penalty, he'd been mostly good to that point in the game. I think a lot of people kind of assume due to age he's lost pace and think he must be much worse than he was, and that because he was always rated before people presume he's on the decline. I always really just thought he was over rated, he's playing fairly similarly but I get the impression he's a strong character in the dressing room and on the pitch. Winners mentality can overcome lack of true quality and drag better performances out of other players and I think that is Demichelis's most useful trait.
EDIT:- hate that bull "you can see they have lots of players between the ball and Carson early in the game......" Hell even Owen got it right pointing out they were leaving two players pretty much in the opposition half... OWEN noticed it FFS. Such crap commentary, which teams when the opposition has the ball get out of the way? Barcelona to grimsby, when the opposition has the ball you try to get between them and your own goal. He was trying to be negative and call them defensive for what is normal football and a surprisingly offensive mentality of leaving two players upfront. We've seen genuinely defensive setups where Mourinho would have everyone including Milito in their own defensive third for almost the entire game.