Played Guardians at Pinfest. I think it's still too early to say if it will be a great game. Iron Maiden seems to be getting the love. You never know with Stern. Updates may be slow or final code may not be great with Guardians. They may focus their efforts on Iron Maiden.
Spiderman is awesome now. Buy it, enjoy it and sell it later, if you want, to get Guardians when the code is done.