My friend has a big home birthday for her daughter every year (now age 10) and has always kept the traditional birthday party games as the entertainment. She does the same ones every year with kids ranging in all ages and it always works out great.
There is always a pinata and every kid gets a swing or two. They line the kids up youngest to oldest - youngest goes first. She always does musical chairs and water balloon toss (you would have to change this to something for friendly for indoors) and limbo. All the kids participate (the older ones seem to enjoy acting young again). The adults sit around and eat and drink. She makes all her own food (with a little help from some family).
I love that she keeps things simple and fun. I have heard of a nice simple goodie bag good for most ages - just a rice krispie treat wrapped cutely in a decorative bag.
Opening presents there is personal preference. I know plenty of people who do it at the party and plenty that don't. There are benefits to both options.