Cosplay- This is the biggest draw for comic con to me, I love both making my own cosplays and seeing some of the amazing work that other cosplayers have brought. I also (mostly) really like the cosplay community, and, whilst I'm still very new to it all, I like seeing the friendships that other cosplayers have made. Plus, there's the masquerade that I simply adore.
Merchandise- This is mainly made up of three things: Sailor Moon merch, which isn't that readily available in the UK, matcha tea flavoured chocolate, and ALPACAS! The merchandise at comic con is just the best thing I've seen, and they have Disney pin lady too.
Guests- Whilst the guests aren't as high quality as the cons in America, I still enjoy seeing who is going to be there. In the short time I've been going to cons I've seen panels, guests signing autographs and even guests doing performances, and some of the guests have been really quite famous. (Dolph Lundgren and Saw, for example)
The general atmosphere- I think that the people at comic con are some of the most inclusive of all the people I've ever seen at any event. No one gets judged for the costume or fandom they belong to, everyone is nice enough when you ask for photos, or when you ask a photographer for photos, and everyone just enjoys themselves. Obviously, there are exceptions, but there are always idiots that try and spoil it for everyone.
These are my main reasons I enjoy going to comic con, but I could probably list loads more. I can't wait for the next one, and to experience ones that I've not been to before, as well as building up some cosplay friends.