Does Tokyo Disneyland have anything for adults, or is it all basically for kids? Disney World in Florida seems to cater to both adults and kids, though different parts of Disney World tend to balance this differently. (For instance, Magic Kingdom vs. Epcot.) One Japanese family I know has basically said that the Land park in Tokyo's Disneyland is more childish, but that the Sea park is much better for adults. But that's just one word of mouth that's hard to research accurately. So how good is it for adults, and does it matter which park you go to or something?
While I don't know any Disneyland except those in Tokyo, I'm sure the answer depends highly on your preferences.
However, just walking there, you can find that there are many, many adults, mostly early-20s and some 30s, who enjoy the Disneyland without children. In fact I can even assume that there are more adult friends groups than the family with children.
Also note that in Japan a lot of women who are 20s enter the Disneyland by wearing high school uniform and enjoy the park just like children. Even those 30s wear the uniform, which is quite nauseous, and I have a pathological hatred for it. But it is generally accepted.
As to the Sea for adults comment, it is true that it is considered that the Sea is better for adults. That is because there are more restaurants that serve the alcohol, and people who likes the Sea tend to prefer the scenery, night scene, restaurants, cafes, and just walking around there, to rides, attractions, mascots, and shops, which are better in the Land.
However, if people say the Sea is better for adults, it usually means the Sea is better for a couple. In both cases, it is boring if you are alone, though I hear some people do enjoy it alone.
I should also note that you can enjoy both in a day. They are pretty close to each other and you can just change the park by taking a monorail. If I remember it correctly, the park sells a ticket to enjoy both in a day.