I think the reason you are so impressed and addicted to LKS is because you had absolutely zero expectations for it and when you finally played it the title met your expectations and then some. I know because it has happened to me. I've found a game that was very obscure only to hail it as the best thing ever.
I don't think this is the case because I have no expectations for any games these days and I'm inevitably finding that I'm still only mildly amused by most of them. As you get older and your time gets more valuable, you can't afford to simply spend 30 hours playing through games anymore, but I'm MAKING time for LKS, something I haven't done in some time.
It has been ages since I've had a game cause me to go to bed late and wake up early. The last time I did that was when the Wii launched and I woke up to play some more Red Steel and try out Wii Sports.
I had only rented LKS through gamefly but I decided to buy it. It's too good of a game NOT to buy.
And the reason I think it's such an AAA title is not just because the gameplay is incredibly fun but because the game is dripping with unnecessary polish: the areas of your kingdom are filled with unique houses, each one lovingly-crafted by a graphic artist, full of detail. You might not even wind up SEEING this detail, though, as you primarily use a system of cannons to navigate the game world.
This is a rare case where a developer went above and beyond the call of duty on a game. There's just so much content here and so much that I'm inevitably missing that I can't help but be impressed.