Now that I've hit 21, I don't think I'll look forward to any of my birthdays like I used to. Birthdays are cool as a kid, because everyone sends you money and you're like "Look at how ~old~ I am aren't I awesome??" And it was fun, thinking about how many years I had to go until my 18th/21st birthdays. But now that I'm a fully legal adult, there's nothing to look forward to. Just another year older.
Typically for my birthday, I don't do much. As a kid my parents made cake, and that was about it, since I got cash for presents instead of physical presents. On my 19th I went out for dinner with friends, on my 20th I hung out with my sister and different friends and had some cheesecake (iirc), and on my 21st another completely different set of friends took me out drinking. I've never planned out a proper party and never plan to. :)