It's quite different than Mickey's Not So Scary. What has you interested in it in the first place? If you don't like haunted houses, I'm surprised you'd want to go to a Halloween event!
I'm not a big scary movie person, but I LOVE Halloween Horror Nights. I (personally) don't find it to be that scary, but your mileage may vary.
HHN takes place throughout the Studios park, and there's usually 8-9 house attractions and a few "scare zones" in the streets of the park, each house and zone has a different story/theme (sometimes original concepts, sometimes based on a movie/TV show). The "scareactors" in the zones and houses will try and startle you, which for me is quite fun (it's also funny to watch other people freak out!). There are also a few shows each year (although their longest running show ended last year- not sure what, if anything, will replace it)... they had a dance troupe (Academy of Villains) as well last year who put on an awesome show!
Overall, Universal puts in a lot of work to this event and the production value is wonderful- fantastic sets, costumes, makeup... I love it from an artistic standpoint as well. Here's a neat behind-the-scenes video to give you a better idea of the event: