Killzone 2 or Star Ocean: The Last Hope. (Purchase Decision)

[BengaBenga]

Killzone 2: Shooter, 10 hour single player, loads of online
Star Ocean: JRPG, 50 hour single player, no online (but new game +)

I would decide on whether you feel like playing online or not.

(SO4 does look like the best console JRPG this gen so far though.)