That's a bit reactionary.
It can be a sandbox without being a WoW clone. There were MMOs before WoW. There will be MMOs after WoW. They'll use some of the same mechanics and do some things differently.
"Sandbox" and "themepark" are really rough descriptions of a game anyway. By many definitions, Skyrim isn't a sandbox. People would call it theme-box, sand-park, open world themepark, ect.
Who cares though?
Ultimately its about a few things for me:
Does the game give me freedom to play how I want to play or force me down certain paths?
Can I explore the world openly or do I have to follow a linear progression of areas?
Is it fun?
ESO seems like it'll do well on the first and third. Still to be seen on the second.