People on the fence about multiplayer should consider that "multiplayer" is not just limited to 1v1 skirmishes or even team skirmishes for that matter.
Multiplayer includes a very broad range of games built using the map-editor. Casual games like Nexus Wars, Turret Defense, Evolves are a fun distraction. I played Nexus Wars for the first time last night and ended up so engrossed that I didn't realize I had been playing it for 3 hours. This is just the tip of the iceberg too - I've heard of Mario Kart re-makes, Metal Slug re-makes and R-Type re-makes being built.
$60 is going a long way for me.