I'm in the same boat as many other posters.....over the years, Epcot has become-by far-my favorite park.
OP, you're essentially correct when you say that Epcot is different than the other three parks, but believe me when I tell you, that difference is a palpable and wonderful bonus-definitely *not* something to be dreaded for fear of missing out on more traditional "Disneyesque" experiences. Somehow, they've managed to maintain that Disney feel while creating a very unique atmosphere.
You've been to Tomorrowland in the MK, right? Imagine how that must have felt when the park opened back in the 70's-futuristic, sort of other-worldly? At least that's how I think Walt imagined it. Well, IMO, Future World at Epcot is the real culmination of that vision. Even though I've been there countless times now, it still feels like I'm visiting the future every time!
As far as World Showcase is concerned, I'm not sure how anyone could find it anything but fascinating. Obviously, every place has its haters

, but each of the countries is so extraordinarily well done, the CM's are incredible, and the food is borderline amazing. I'm not sure how *anybody* can say that they dislike the entire thing. There really is something for everyone.
I'd be willing to bet that if you love the *other* three parks, you'll find that one day at Epcot is not nearly enough on your first visit there. Hope you have a great trip!!