I always hope/aim to get more hours out of a game than each £1 (about $1.60) I spent purchasing it. The only game recently that failed to meet that was Super Mario 3D Land, which I've clocked about 18 hours in iirc, but purchased for about £25.
For example: some of the other games I've purchased in the last 12 months.:
Xenoblade Chronicles - £35 bought, 102 hours played
Mario Kart 7 - £30 bought, 54 hours played
Zelda: Skyward Sword - £45 bought (Wii Remote + bundle), 51 hours played
Tales of the Abyss 3D - £38 bought, 46 hours played
SMT: Devil Survivor - £20 bought, so far 18 hours played (but I'm nowhere near the end)
Final Fantasy XIII-2 - £22 bought, 35 hours played