We spent two days last week at the Great Wolf Lodge in Traverse City...what a blast!  We played most of the first day, checked in, stayed overnight, then played until lunch time the second day (that's plenty of pool time, I think). 

The hotel is really nice, and the water park is awesome.  The only complaint I have is that we were told (during the telephone reservation process) that our room would be ready at 1pm...we couldn't get in it until after 4:30pm.  That's pretty poor, because the kids needed someplace to go before then...otherwise, a very good time.