Ok I'll start.....
I've been to Goa 5 times in the last 4 years and spent equal time in the North and South.
South Goa as you have probably guessed is a LOT quieter than the North.
I didn't like any of the 'resort' areas - Colva, Cavalossim and all the secluded 'mega' hotels which you can't spot until you are very close. Great part of Goa to rent a bungalow.
I stayed at Benaulim and loved it. There is so much beach to walk or cycle along, if that's your thing you will love it. Also loads of country tracks to explore rural life, nice and flat to cycle and if you go before 11.30am not too hot.
I found everything to be a bit cheaper apart from Taxis. Food definately.
If you are looking for action, you won't find it in the South. Relaxation yes!
Nothing like the Aguada - Baga 'strip' feel, more like a longer version of Morjim and further North.
The South attracts those who want a bit of piece and quiet although Colva was like a minature Calangute to me (Lager, Curry and Chips).
I think you would have to do your research on where you are staying if you want to stay for any length of time as you may want to move around.
I've heard people say there wasn't much to do, but then again if you want to chill out and relax ideal.
My love affair with parts of North Goa (Aguada to Baga) has finally gone unfortunately, maybe I will return to the South but not next year.
If you have any specific queries I can reply.