Hi Lesley - We go up there almost every year & stay in one of the cabins for the weekend, but although they have parasailing, we've never gone. We do rent the pontoon boats, though. They're a bit on the pricey side, but fun to take out on the lake.
I do like the bobsleds at the Alpine Run - those are fun, and they do have a mini zoo up there that we've visited. Across the lake, by Fawnskin, there is a nature center, I think, with maps of trails. Also, in the neighborhood behind the McDonalds, there is a beach on the north corner of the houses, where they meet the lake, and there is a swimming area in there.
Can't think of any killer restaurants up there since we usually cook our own.
Have a great time! (If you drive to Lake Gregory, there is a big waterslide you might want to try out, as well as water bikes, etc., that you can rent - much smaller than Big Bear, though)