Yeah, Jess, I'm on PC as well. I'm not sure, I haven't had any problems with it. I'm sure there may have been a fix at some point if it's not up to your computer.
There's a handful of new content including new classes, maps, monsters, and even better rewards. There are two new difficulties as well, Nightmare and Heartbreaker (Being the hardest).
I'm having fun with it at the moment, the new map "Ferelden Castle" has a Dragon boss at the end it gets pretty difficult sometimes.