Interestingly Better graphics lowers my chance of buying the game. I have three kids each with their own PC - if a game cannot run on all three I wont buy it.

The costs of maintaining the three PCs is high and therefore I only buy components that are in a decent price range. This means that the hardware used on the oldest of the three PCs was cutting edge 5 or 6 or even more years ago (Celeron 2.4, 256MB, Geforce 440 MX).

Secondly I only buy games that will suit the family so basically they must be:
1. Educational
or
2. Strategy games with Network play options
or
3. Sim games (eg Zoo Tycoon)

Because thats what our family plays. (Ever seen a 5 year old play Age Of Empires - they have no idea what they are doing but they do it anyway and enjoy it).

I pretty much only buy bargain bin games