Isn't November on the tail of end of monsoon season? I've gone there several times in December and only had a bit of rain.

Rainfall

I haven't been to Ko Samui, though I heard OK things about the moon festival from friends. Was in Krabi during the tsunami. I generally like the area, stayed in Ao Nang beach and went to Railey to rock climb (they got hit the worst by the wave).

Going from memory here.......for Ao Nang, it's a small, OK beach due to boat landings/ferry area. Beaches have no chairs or anything. Not much nightlife. Railey was more family orientated, only a single hotel I think. The beach next to Railey was more "relaxed" (think younger crowd, rock climbers......more like the movie The Beach).

It was good change from Phuket, but I think Phuket might be better for a honeymoon only because it might have better hotels for honeymooners, more things to do.

Just my .02