I did Tae Kwon Do for five years - ignore what you saw in the Olympics though, that was in general incredibly boring!
Tae Kwon Do is all about kicking, generally to the head and body, with quite a few jumps etc. thrown in for good measure.
It's cracking for fitness and stretching...not so good if you actually needed it in self defence.
The lack of emphasis on punching, take downs and defense (though there was some) hobble it as an all rounder.
Building your personality and be more disciplined etc. depend on two things:
1. Actually going - if you're not disciplined you may not actually be bothered to get there
2. The instructor, I've seen some instructors who are as strict as they could be. That works for some people not for others.
Personally if I'm going along to learn something I don't appreciate being shouted at, not being able to talk etc., so the best idea is to approach some of your local centres and just watch what's going on and see what you like.
Thinking about it, I'd love to learn Jeet Kuno Do...may have to look into that.