Much like "nerf," these are two terms that have been beaten into the ground until they no longer have any intrinsic meaning. The original "themepark" game was freaking EverQuest, which is not what anyone thinks of when he uses the term in a more modern sense. There's more concern given to whether or not a game fits into a given category than whether or not it's actually fun to play.
And that is a bad thing. Sure, your sandbox features a great housing system, but so does The Sims 3, and the latter doesn't abandon me in a featureless wasteland that eschews actual content in favor of letting me choose my final destination (here's a hint: All those destinations are grinding). Yes, Mr. Themepark, I see you chuckling in the background, but your single leveling path followed by the exact same huge-group gear-grabbing jamboree is not better, just annoying in a different way.
That's why I play Final Fantasy XIV. But I should probably elaborate a bit on that.