Oh, dear...
Before I start - what's the difference between character development and out-of-character? This is in regards to Vetinari. I think he's just changing, personally (but I am new to the Disc).
Anyway...
It actually took a couple of months for me to get into it (I bought it, started it, got bored, put it down, read something else, saw it sitting there and picked it back up again) but by the end, I couldn't put it down. Funny how that happens. But I don't think I would read it again. Admittedly, it wasn't a masterpiece in my opinion (some of it paced strangely, some parts which were meant to be a payoff didn't quite ring with me, etc.).
'Drunk' Vetinari made me weep with laughter. I thought that the scene began with him being more talkative than usual at the beginning and suspected something was up. However, his story about watching mother feed babies with mother and babies was chilly, a weird moment of darkness in what was usually a light-hearted novel, but it's one of my favourite bits. I also loved Nutt, I think there's a lot of room for a lot of development in his character.