my girlfriend and I went to sixflags 2 weeks ago and had a blast!

you're right about the heat and humidity... but the lines were short for us. the longest we waited was about 10 mins. & most rides were only about 5 min wait. we went on a weekday, so that probably had something to do with it.

gotta try the batman inverted roller coaster. sit in the very front seats... it's worth the extra wait!]

and take a picnic lunch with you... they have picnic areas near the parking lot. they'll let you re-enter. it's alot cheaper that way (a hotdog, chips, and coke will cost you about $8 in the park)

and take a backpack with some bottled water - water is $3 for a tiny 10 oz. bottle.