I have attended this for the past couple of years and it is awesome. Huge -- they had over 50,000 people last year. Hundreds of exhibits, mostly by people or small clubs, show off cool things they have made. A little art, a little science, a little magic. Fire, electricity, and some serious welding skills.
The site gives details. I think they make it seem like it's for kids (and it is a great event for them) but really, it's for anyone. Plenty there to interest adults. The video (scroll down the page) does a good job.
I wouldn't miss it!