Few RPG's really allow you to influence the world, MMO or otherwise. In single player RPG's its all mostly scripted. But to your point: The "themepark" moniker for MMO PVE is widely used. I simply have trouble believing its origin is not derogatory and I cringe when I see it used. BTW that was a shocking measured response for Dart! Who's using your account?
It was certainly more measured than your heavily biased response, so maybe we switched accounts by accident?
I mean, you're always so amiable and level-headed!
You said all video games are themeparks - and if you think about games like Mount and Blade, Civilization and so on - you'll find why that's not the case.
As for MMOs, games like EVE Online, Darkfall, Mortal Online, Ultima Online - and so on are almost pure sandboxes. Simply because developer content is so limited compared to the amount of player control and how that control is driving the gameplay.
I'm sure lots of people use themepark in a derogatory sense - but I don't. I've greatly enjoyed several themeparks - and the overall quality of the genre tends to be much higher than the average sandbox.
My personal "ideal" MMO would be a genuine hybrid - as I do love the concept of a sandbox, but I don't like having to create the games for the developers. I need high quality content as well as freedom to influence the world. I'm still waiting for such a game
That said, ArcheAge looks like it's the first game to feature close to 50% of each feature-set or design paradigm. Hard to tell until I play it - but it's looking to be the most promising MMO in many, many years. To me, that is.