Hi there. I actually live in Japan and have been to both parks more times than I can count.
I LOVE TDL and TDS but be prepared to wait. As long as you are prepared, it is a great experience. There are quite a few rides that are the same as WDW. TDL is quite small land wise but quite compact. There is a lot to see in both parks. I would recommend at least one day per park.
There isn't a one-day park hopper style pass here. If you buy a three or four day pass then you can park hop BUT only on the third and fourth day. The first two days you can only choose one park to visit. The wait time can be INSANE! There are sometimes an hour wait for popcorn! It REALLY depends on the time of year that you visit. If you visit during the first week of May (It is called Golden Week here because EVERYONE in Japans has a week holiday April 29th to May 6th), the park is actually closed for short periods due to it is filled to capacity. Also During Aug 10th to the 17th, another National Holiday week. The wait time for the lines get to the point where the CMs old up signs with the time in hours not mins.
There is some great shopping BUT get it done early! by the end of the day, the shelves are empty! It is a tradition here to buy souvenirs for everyone back home and the dog too! So by 5pm, the stores look a bit bare and the wait to pay is almost as long as the ride lines.
Fast passes are almost gone by the second hour after opening. So get there early. Or pick the few rides that you want to go on and RUN!
Do you plan on staying at a Disney hotel? There are some really nice partner hotels that are actually closer in distance to the parks than some of the official hotels. There is simple (but not so simple in price) hotel right near the train station. It is not listed as a partner hotel but it is directly in front of the shopping center Ikspiari. It is called JR Dream Gate Maihama. Here is a link:
http://hotel.eki-net.com/e/dreamgate/index.html
Sorry for being so long winded. Hope that all helps. If you have any other questions, please feel free to ask.