NYNY and arcade at Fremont street for Pinball, PHOF is worth a visit if for nothing else then for ultra rare machines like pinball circus.

+1 for red rock canyon area for hiking, and hoover dam. I also did with my friends a day trip to Grand Canyon, lots of driving for one day but definitely worth it if you have an extra day (5 may not be enough though)

Show's are a must too, I'm a big fan of Circue du Soleil shows of which there are many. Ka at MGM is action packed, O at Bellagio more artictic but they all are nice

Talking about eating - so many great restaurants in Vegas but if you willing to try a different kind of culinary experience check out heart attack grill. Quadruple bypass burger has ~8000 calories and Customers over 350 lb (160 kg) in weight eat for free if they weigh in with a doctor or nurse before each burger.

There's no bar in the arcade area, but Vegas is all about wondering around with a drink in hand. And the bigger the better, frozen margarita's can be up to 64 ounces...