Well, you can go to the DVD display in Electronics and get a photo-op with Spidey, where he appears on your phone when aimed at one of the display panels. Spidey also spouts some one-liners and will shoot web at you if you touch him on the screen.
But the real fun happens when you hold the cover up to the app. Spidey and The Lizard come to life and fight on top of it! The building they fight on moves with the cover, so you can recreate the Adam West Batman effect by turning it on its side!
There was also a van tour a while ago where you could use the app to see Spidey and The Lizard have the same fight as the comic cover, only atop the tour truck instead of a building.
But, of course, there's the Webslinging game, the real attraction of the App where you can blast people with Spidey's webs. There is a basic "practice" mode which involves simply firing your webs around for a fun effect by tapping where you shoot.
But then there's the game, where you use your webs to deflect various lab equipment the Lizard hurls at you. However, then the Lizard appears and breaks Spidey's web spinners! (Yeah, the original Spiderman used mechanical web-slinging devices; they weren't biological until the movies. Peter Parker is a genius, after all.)
So now You've got to trot around the store taking pictures of the displays to repair Spidey's web shooters. I've found three of them, but the Kellogg's sign has yet to be found. Apparently you can play with just one shooter repaired, but I haven't tried yet.
A word of advice, this game is many, many megabytes big, so I'd say download it through the iTunes on your computer, rather than trying to grab it in the store, as mobile devices don't like having to handle more than 20 mb at a time.
Either way, the effect on the Comic Book which you can take home and show off is fun enough by itself and well worth the $3 needed to buy the book (Though you can try it out in the store for free) and you get a decent comic and preview DVD for the deal. All in all, "Webslinger" is a pretty fun app and I hope to see variants of it more in the future.