I've been 4 years running, though sincerely doubt going this year (relocation and stuff)....
It's a good chunk of fun, though I go for different reasons, mainly to ride the rides (the good ones) at night and for the price of one ticket, get to go to both Universal and Islands of Adventure. And the park stays open till 2am (official Orlando shut down time).
They usually have 6 haunted houses, 3 'good ones' are so, but the lines can be terrible for the houses, easily 90 minutes. Which is basically what you do, go to ride-haunted house-etc. In the walkways and stuff guys 'pop out' with fake chainsaws and stuff and try to scare you. The novelty wears off very quickly though, and they always pick the people that are going to majorly overreact too, I don't mean any offense, but 90% of the time a black teenager.
Great to go with a group of friends, and a girl/guy you're interested in, and have them hung your arm all night.
And oh FYI, they have drink (alcoholic) stations all over too
Though they're hugely pricey.