So even though MK is similar to
Disneyland (which we have been to) and the other parks are so much more unique? Is that because there is so much to do in MK compared to the other parks? Are the other parks easy to do with 1-day each?
There's a lot more to do and see at MK than DL IMHO. Even though some rides are repeats, i.e. Space Mountain, some are actually different, i.e. Pirates, Winnie the Pooh. Some of just fun and you don't mind repeating them at both parks. There are also just a bunch of rides at MK, in addition to shops, food, and shows.
It also depends upon what you like to do. If you like thrill rides, then DHS is good, since it has Rock n Roller Coaster and Tower of Terror; however, it doesn't really have that many other rides. If you like shows/musicals, there's a ton of them at AK and a decent amount at DHS. The World Showcase at Epcot is really cool, and I could spend pretty much a whole day there; it doesn't open until 11am though. However, DS8 can only do a half day in WS. I think MK is the best all around park and really has something for everyone. That's probably why it's a good repeat, but it's hard to do everything in a day and there's a lot of cool stuff to repeat.
As for time in each park, our first time, we spent 2 days at Epcot, 2 at MK, and 1 each at DHS and AK. We did do naps though on the Epcot and MK days. Now, we've been there and done that, so we don't do every attraction. DHS and AK are half day parks for us. We don't do water rides and don't like the musicals. DS is just starting to get to where he wants to do some of the bigger thrill rides, but DH and I don't really like much beyond Space Mountain.