I first learned about Newgrounds around 2000/2001. It was a new site at the time and I saw a lot of it's Teletubbies features and thought they were hilarious.
Several years later, I, being interested in animations join Newgrounds.
I must say what I enjoy most are the people and the spirit of the community. Reading the comments on some of the Flash Animations is great, I love sending a PM to Egoraptor and *gasp* actually getting a response, and the best thing I saw was the author of Bambee becoming an animator at Dreamworks. I only hope I can ever be as successful.
What I would change if I had one day? I honestly can't think of anything, I love the site and I would only do more (Post on forums a lot, review a lot of content). I wouldn't specifically change anything with Newgrounds. Newgrounds is what I know and love.
What I miss: Waiting eagerly for a new Decline of Video Gaming. Those really got me into Newgrounds and animating and I sincerely miss seeing a new one every year or two. It was great while it's lasted and I sorely miss seeing it on the Top 50. I am VERY excited for Tarboy 2 however...