Alistair's swooping did fit the character. As someone pointed out, he got all funny and juvenile to hide his insecurity and how he felt that the whole darkspawn thing and responsibility he got was way too much for his stature. It was done elegantly and subtly enough that you guys apparently didn't have a clue about it having skimmed through his dialogue or not using him at all - or not having actually played the game.
You may not like him, but Alistair was actually a good character, one of the better ones in DA:O. It really doesn't make much sense to take some of his lines out of context and go all "LOL bad writing". Actually you never, ever take things out of context when going for any sort of qualitative analysis, unless you're trying to analyse how things work when taken out of context. A lot of sentences you exchange with your friends every day would make you look like a hardcore moron if taken out of context.
Also, DAO wasn't subject to medieval stylisation. The only character who used all these 'tises and whatnot was Morrigan, and it also felt right (could be done better, of course). She lived her whole life in the wilds and most she knew about the world and people was from the books she read: this was reflected in her language and her stunted empathy, inability to cope with emotions.
I think Sten's cookies were resembling an easter egg. There were quite a few tounge-in-cheek moments in DAO, like Sten's "exchange" with the dog ("You are a true warrior, and worthy of respect"). It's obvious that these are comic relief.
A poorly written character in DA:O was, for example, Loghain. It was a neat concept: considers the king a moron who will doom the whole kingdom, picks the renegade option. Trouble is he seems schizophrenic. He never seems to have any doubts. He's generally too unreasonable and muahaha villain-esque for the machiavellic exposition to really work - and being muahaha villain-esque and unreasonable also doesn't fit his personal history as a brilliant tactician. The "Ostagar maneuver" was just plain stupid.
Now, imagine that he arranged regicide instead and took over before Ostagar. The player would have his suspicions and gather evidence to finally expose him as a murderer in the Landsmeet, while Loghain would pretend to be an ally while actively trying to hinder and assassinate the Warden the closer to the truth he got. That would make a much better and believable Loghain.
As to DA2, banter also doesn't really serve as an example of poor writing. It's ALL tongue-in-cheek. The apostitutes joke kinda fit Isabella's character, which I guess was meant to be Jack Sparrow with huge tits. The problem with most of DA2 characters was that they were exceedingly shallow and one-dimensional. They kept the same routines all the time, and even Merrill's blood magic quest didn't help.
Fuck, there simply is NO character development in DA2. In DA:O characters evolved over time as you gained their trust and stuff happened around them - well, most of them did, except for Wynne and Oghren. In DA2 Merrill does all sorts of terrible stuff only to go on an idiotic rant "OH MY WHAT HAVE I DONE THEY ARE ALL DEAD OH MY OH GEE OH MY" and you can't even fucking kill her. God, I really was longing for a [kill her] option, but no, no dice. Not a way to kill an annoying elf which stupidity led to endangering her whole clan, you have no other option than murdering dozens of innocent Dalish. Just so that the annoying elf can weep more and all you can do is imagining raising slowly your hands and slowly strangling her to death. Fuck.
And even when she goes through all this some time passes and - oh, I just murdered my whole extended family but we've business as usual, right? Why would she ever stop being a whiny double-check-where-you-step annoying elf after commiting genocide? No reason at all. It's perfectly fine to keep making sweety-sweet jokes after trauma like that; Bioware fans can convince themselves that it's a coping mechanism.