I feel like if there was anything to do in Tokyo, I have done it! and in 2 days!
The thing about Japan's capital is that it's not so much that there are attractions to visit, it's more that you just need to wander the different districts and be an excellent people watcher.
In 2 days David and I managed to visit a lot of the main areas: Harajuku, Shibukya, Sinjuku, Odaiba, Asakusa, Akihabara, and we stayed in Ikebukuro in a ryokan (traditional Japanese inn).
Again, the rail pass was great to have since you can take the main JR line which loops around the city which makes it so convenient in this complex metropolis.
Tokyo looks like any other major city but has character, lots of it! Each area is unique in its own way and has something to offer.
My favourite place was Odaiba which is a man made island in Tokyo Bay. The view of the bay is stunning, esp at sunset and you have to take the monorail to get there.
Eating and actually doing things are a bit pricey in Tokyo so people watching is a great and economical way to get to know
this place.
The Imperial garden which is close to Tokyo station is also another great sight. We had a nice picnic since it was another hot day.
2 days flew by in a flash and these days were spent walking and jumping from train to train. It seems like all people do here is commute. The main difference in Tokyo from Seoul is that people are a bit more mannered. There are signs on the trains to not talk on the cell phone and to keep it on vibrate. People also seem to be generally more nicer and helpful as well.
Tokyo is a very developed city and its easy to forget you are in Asia when you are here.