Marvel Legendary expansions

So today was my birthday and I spent the evening playing games with some good friends. One of which being a gift from said friends; Marvel Legendary.

We've only played through the suggested tutorial set up, but so far I'm impressed! It combines my love of all things Marvel with my love of Dominion, but it's different enough to bring an extra level of awesome to it.

I'm so excited to play more and perhaps get some expansions for it. For those that have played, are there any particular expansions that you consider to be awesome or a "must have"?

Any advice, thoughts or discussions of the game are welcome!