] Well, I don't think NA is darker or like a Bronte novel. It is a parody. I read somewhere that NA is 'the most youthful and optimistic of Jane Austen's novels.'

I must agree. It is only Catherine that tries to make it dark by her reversion into Gothic mode - when herlife quite blatantly isn't!Bless that girl.
NA is very full of wit, especially by having Henry Tilney's quips and observation, as well as us laughing at Catherine, Mrs Allen, etc.
If you think about it, there is less "shadow" in NA than P&P (not that there is much in P&P, admittedly).
I guess that the thing with NA is that it is similar to the juvenalia in so much as there is copious amounts of spirit and sport; P&P toned this down a very little to make it universally enjoyed, where as some find NA a little ridiculous at points (so I have been told).
NA is, we must conclude, an aquired taste that we are priviledged enough to have!