If you're looking for thrill rides in general WDW isn't really your best place to go. I love AK it is my favorite park right now but I even recognize it isn't a full park. Yes there is 18 attractions but those 18 attractions don't work for everyone.
But that's true of all of the Disney parks. In my case, with people spanning from age 5-45, we can still hit just about everything in a park. However, if it were just a group of adults my age, then none of these parks are really full day parks. MK only has about 7-8 rides that appeal to adults. It is the blend of appeal of shows and rides over multiple age groups that really makes these parks multi-day attractions. DHS has lost that with all of the recent closures, and EPCOT has been there for years. AK really holds up much better than both of those parks, and Avatar will only add to that, while the other two continue to crumble.