Darkspore.Its TOTALLY playable and not forgeted by EA making it online only for something that is almost only played singleplayer because the coop is dumb!
warframe, it's a grindy co-op with some mmo elements, but the grinding process is funbut if you want full out grind which you could probably play in the background, runescape
TESO: Tamriel Unlimited is also quite decent for storyline and story-based quests. The grinding is pretty minimal for gear/experience/skills too. It's not free to play, but has no subscription.