I've seen dead island in the $20 or under box at a local store and debated on getting it, worth the buy?
It is still worth $60. It is open world, you have Main quests, side quests, and on going quests. The Main ones are for the story line, and every few main quests you unlock what is similar to what I'd call an outpost. People in the outposts need things, like people saved, lost things being found, supplies, etc. These are side quests. You can do these for fun and the are IMO the best missions in the game. On going quests are ones that you don't ever finish. An example of this is there is a quest where this girl needs water, you give her water bottles you found around the world and she pays you.
All the missions have an XP reward and an item, like a new weapon, weapon mod's, blueprints etc.
You kill the zombies and some can be looted, there are different types, I'll let you discover what they are. Weapons can be found all over the place.
Overall it is like a 9.9/10.