While having access at all is nice, the terms of use are prohibitive and somewhat heavy handed. They basically say you can make something, but can't charge for it in any way, you can't create a mash-up (no augmentation of data) and if it works out, Marvel will probably implement it for themselves anyway. Not really as 'open' as you might hope. The following default rules apply to all Apps: Advertising. No advertising…
They never said it was open, so I don't see the problem, unless you readily associate "API" with "open".
Especially when talking about the kind of API most likely to be used by clever teenagers on a fansite.