T.
i've taken my 3 1/2 year old daughter there a couple of times and she LOVED it! so did all of her little friends that we met up with there. the area was clean and when we went, on a weekday in the winter, it wasn't super crowded at all. i would imagine it would be more packed now. if you didn't want to go through the obstacles with your grandson, you can easily see him through the netting (unlike at some fast food play areas). they also have food and tables to eat at.
definitely check it out during the day, even if it isn't the right place for a birthday party.
i'd also highly recommend boomerangs
http://www.boomerangspartyandplay.com/locations/boomerang...
although i think their prices for parties are a bit high, their regular admission price is very cheap. and they have papa john's pizza and other great snacks. we've been there from 10:00-2:30 before.
good luck!