Must see and dos in Tokyo?

I am planning on visiting Japan this summer (July/August) but I'm not sure how long I'm staying in Tokyo so any suggestions on what I MUST do/see?

I'm very interested in cosplay, fashion, parks, nightclubs, karaoke, hotsprings, in general having fun. Also I want to taste specific Japanese food but not waste half a day waiting in line for it.

Thanks for your help everyone! I really appreciate it!

Some suggestions:
http://www.japan-guide.com/e/e2164.html

DO, spend a lot of time in each part of tokyo (like at least a day in each part)

DONT, rush around and spend 1 hour in shinjuku, 1 hour in shibuya etc as you dont see anything by having "rush holiday"

What are you into to start off with?
What age are you (or ruff age)

There is so much to do in tokyo its very hard to start.
Do you want shopping?
Do you want to try differnet beers?
Do you want to go to the fish markerts?

Let us know abit more and we can help.

3 days in Tokyo are good and enough for an average tourist with limited time. Of course you can extend or shorten it in accordance with your interest and plan.

If you go to stay in Tokyo, do not miss nearby sights such as:
- Kamakura
- Nikko