Yeah, it wasn't anything mindblowing, but it was definitely fun. It's good preparation for the insanely spirited Welcome Week (which I'm sure you'll all be part of!!).
I also remember there were 'workshops' that help in kind of outlining some of the problems you will face in university, and what steps you can take in overcoming them. There are also "leadership" type workshops -- which aren't too different from any high school type leadership camps, if you have been to those.
It was also just an all around fun time. When I went, there was bowling, a dance competition (Alex was amazing at that), a couple really cool guest speakers, a dance event at Charlie West, and I remember this one manhunt type game in the Student Centre that was pretty cool.
You also meet a whole lot of people! Like during the school year I would always come across people again I met at Horizons. And it's a really great icebreaker, just saying "hey, were you at Horizons?"
It's a definite recommend from me... but if you already are really comfortable socially, not too worried about the university transition, and are familiar with the Mac campus and lifestyle, I would pass.