I lived in Summerlin for a year (and Las Vegas area for 5yrs) and pretty much ate the whole time. SOOOooo many great restaurants because there isn't anything else to do there.
DON'T eat the standard stuff! It's like being in a wonderful food oasis there!! BJ's is just BLECH! Like a Chilis or Applebees...
We love Flemings Steakhouse, Via Brasilia (all you can eat meat!), and Marche Bacchus. Agave for Mexican food is pretty great.
Love the JW Marriott - we used to go there on our "staycations" try their Breakfast Buffet if you have time - it's only $20! And we enjoy their Waterside Grille fresh burgers and wraps.
Grimaldi's Pizza is the best West Coast pizza - I used to work in poker and everyone that came out for the World Series ofPoker from East Coast always fell in love with it. Amazing desserts too, can't go wrong with ANYTHING here.
My friend got married at Vinter Grill and there food is amazing and they have patio and outdoor but covered seating.
Have you been to Tivoli Village? It's modeled after a town in Italy and just adorable - you can walk around and find some great restaurants there and Brio is always a great idea - plus they have patio seating. You can wander there and find something for everyone.
Eat Eat Eat in Summerlin should be their Official Town Motto