Every team and style of football needs a different kind of keeper, or a keeper with particular strengths. Though Guardiola looks a bit silly now with Bravo, he was quite right in his logic; he wanted a keeper good on the ball because that suits the possession football he wants to play.
So what kind of football do we play/want to play? What are our weaknesses in defence that a keeper can help with? As many have said, every season there's a keeper playing for a team near the bottom who looks brilliant, because ultimately he's facing 4 times as many shots as teams at the top. And any good shot stopper looks fantastic in that situation. I myself am guilty of falling into this trap, as I championed us signing David Marshall a few seasons ago. And though he would have been an improvement on a faltering Howard, I do not believe he'd have been as good as Joel is at the moment.
Personally I think our biggest weakness is defending crosses and aerial balls. Our centre backs aren't that tall or good in the air -- we really miss the towering Distin -- but ultimately we don't face too many shots on target as Koeman has us well drilled and we're clearly defending much better as a team. So I think we need a keeper who will dominate the box and claim crosses, more than anything. Additionally, given that our keeper can often go 30+ minutes without having to make a proper save, we need a keeper with great focus.
And thankfully that is where Joel has been excelling. Stek began to look very poor as he lost confidence after the mistake against Boro at home, though it was a foul to be fair, he was weak in the air and bullied by Negredo. It went downhill from there really and he didn't seem to leave his line to claim when he could, and then at other times, he leapt off his line and messed it up horribly. Joel has come in and he's plucking most things out of the air. He's shooting off his line but he's almost never getting it wrong. And, as shown in our last two games, he's managed to go a long time without having to do much and then (both at 0-0 and 3-2 in the game before) he's made fantastic saves at the most crucial of times. And I think they were the biggest factors in us getting 3 points and then 1 point in those games. Potentially 3 points we may not have had with a weaker keeper.
And yet some fans still don't like him. To them I ask who could we get who suits our needs more? We don't need a flavour of the month Hollywood shot stopper. Who out there is doing a better job than Joel at claiming crosses and pulling off saves when he's had nothing to do? However that isn't to say Joel's form is permanent, or that he's suddenly Neuer. But certainly he's doing everything he can to be number 1 for us. Give Joel a chance.
tldr; Open your minds, hearts and rectums, and just let big Joel in.