My problem with Tywin is that before we are introduced to him and when he's not around he is presented as this larger than life, almost mythical character. Yet when we do meet him and get POV's close to him we find out he's just an ordinary man, with just as much flaws as anyone else. Don't get me wrong, he's very intelligent and an excellent character but he's nowhere near as intelligent as characters such as Tyrion, Littlefinger and Stannis. Even Robb, a 16 year old boy is a much better military commander than Tywin, but that's just in his blood.
I don't see this is a problem. I don't know about Tywin being less intelligent than any of the above, either. I mean what are we measuring it by? Baelish is certainly the most cunning, Tyrion is savvy as fuck but Tywin didn't get to be where he did by not being smart. He just had flaws. And they brought him down. But Tyrion, Littlefinger and Stannis have flaws too. And it's definitely gonna get them killed.
Mance Rayder is Mance Rayder. There's no reason he can't be who he said he was. It's not like he's hailed as the greatest swordsman ever, and I'm pretty sure he'd have been recognised by someone at the wall/someone ever. It'd be kind of cheap for Mance to be anyone else, anyway.
Don't see the Martell's as morons at all. Honestly, not sure even Doran could have seen his son would go and try and tame dragons. TBF he had actually succeeded with one, too. It was the other that fucked him over. So while he was an idiot he did have some skill, actually. But yeah. Oberyn was caught in a revenge mission. I don't think you can expect anything ratonal there and at the very least their idiocy is matched by pretty much every other house. House Tyrell seems the only house to not have fucked up majorly yet or have a real idiot? That'll change when they march on Connington, though. They're already underestimating him.
Favourite characters are easily Theon, Oberyn, Arya and Jon Connington I think. Connington's chapters in Dance were great.