About midway into the latest X-Men flick, Bryan Singer’s generous, delightfully convoluted “X-Men: Days of Future Past,” there is a prison break so exuberant and uncharacteristic of superhero movies that you sit up a bit in your seat. You feel the audience around you snapping to. Not because Singer’s return to the 14-year-old film franchise feels undernourished (it doesn’t). Or what comes before seems perfunctory (it’s not). But because the sequence — Wolverine, the Pentagon and “Sanford & Son” — is so eccentric you’re reminded that a little charm has been in the contract between audiences and superheroes all along:
Oh, right, it’s supposed to be fun.