My first one was in 2008, when I was a high school junior. On one hand it felt good to be there with the one friend I was out to, and I ended up feeling really close to him because he spent the day dealing with me and my big swell of emotions.
On the other hand, I felt kind of invisible still, and like I didn't really fit into the wider queer community. There wasn't a lot of bi presence, and there seemed to be a bit of an undercurrent of that being seen as "cheating." Even if I don't identify primarily as bi anymore, that still leaves a bad taste in my mouth all these years later.
And then some kids were canvassing for Obama support as well, and that made it feel a little weird. Not bad per se, just weird.