COD4 for $20 is a steal. Get it.

The single player mode is short, maybe around 4-6 hours depending on difficulty, but it's very engaging. It takes the COD formula (which is a rail shooter at heart) and pushes it to its limits with a compelling story, hectic firefights and varied gameplay.

Multiplayer is.. alright. Trust me I know it's fun but there are way too many knife rushers and SMG spammers. Not to mention Martyrdom users (drop a live grenade when you die)! However i'd be completely lying if I said I didn't lose myself in that game 8 months ago. Worth $20? Oh heck yes. Will its appeal to you last as long as you want it? Now that I couldn't say.