I typically have a rule of thumb where I will not buy a game if it projects to cost more than $1 per hour of gameplay. I purchased Borderlands for $59.99 ($69 something after tax) and I did get about 70-80 hours out of it, so it was worth it.
Dragon Age I paid a full $90 for after tax for the limited edition, but I passed 90 hours of game time about 12 hours ago and I'm still going. I got L4D2 on sale for $40, and I haven't hit that amount of playtime yet, but I'm getting close.
If a game is only going to give me 10-20 hours of playtime I'll most likely rent it, like I did with Halo 3: ODST... rented it for a week, which cost $7.99, took me 9 hours to beat the campaign on hard while exploring, and took it back. Still meets my $1 per hour requirement.
Dragon Age I paid a full $90 for after tax for the limited edition, but I passed 90 hours of game time about 12 hours ago and I'm still going. I got L4D2 on sale for $40, and I haven't hit that amount of playtime yet, but I'm getting close.
If a game is only going to give me 10-20 hours of playtime I'll most likely rent it, like I did with Halo 3: ODST... rented it for a week, which cost $7.99, took me 9 hours to beat the campaign on hard while exploring, and took it back. Still meets my $1 per hour requirement.