Skipping a park, for me, wholly depends on the ages (and for that matter maturity levels) of the guests in question.
Little kids might enjoy some of the more youth-targetted areas in MGM and AK, so for them, Epcot with its seemingly-endless World Showcase wouldn't be a whole lot of fun. I'd personally skip AK, as I've never found more than Everest really exciting (until then, my family used to have to FORCE me onto Dinosaur and even then I was all "No! I get it! Scary Dino! Good Dino! I get it! I'll watch Jurassic Park now let me leave." ((I was rather petulant)))
The group of friends (all of us are college aged) I went with, one of them (a 21 year-old self proclaimed Disney-magic-lover, and Tink fanatic), hated MK. We spent 6 days of our 10 day trip in the MK for at least part of the day, but by the second day, she was done and just kept going to AK, where the rest of us couldn't be dragged. Part of the allure of the AK is likely the safaris, but growing up in Central NJ, I've done the Six Flags Great Adventure safari enough times to know I don't love safaris (though I did one or two of them in AK and they were plenty nice).
SO! IN LONG WINDED CONCLUSION! It really seems to vary from person to person. Me? I'd skip AK - I'm not an animal person and for such a huge park, there isn't enough there that interests me. Epcot probably bores younger children (though admittedly, I could not find that much to do in Epcot this trip). MGM is awesome but in desperate need of new attractions. And I guess not everyone wants to live in the MK, but I think they're crazy.
-Nick