I liked Mad Max and think it's well worth the four bucks. It's mainly the same thing repeated over and over but the world has some cool bits to explore, the car fights are fun and the only place where it seriously stumbles is that stupid race track bit that's feels out of place even for a game that's 70% automotive combat. The story is trash so you don't necessarily need to feel obligated to complete it. Drive around, beat up War Boys, take a bunch of bitchin' screen shots.
I liked Mad Max b/c of its graphics quality, performance (runs great on anything somewhat modern of a system, it seems like), game mechanics (combat's awesome, vehicular or on foot) and the Mad Max IP/setting - but that's another open-world game that I've also thrown to the side and haven't finished.
So many open-world games on the market, it ain't funny. In particular, this game really takes a lot of the stuff from Avalanche's JC games (open-world stuff w/ side-quests of destroy-a-thons, kill-a-thons, and collect-a-thons everywhere) and Batman: Arkham games (Arkham combat) - all games, which I've had my fill of, for the time being.
Hell, that's not even counting other open world games like Sleeping Dogs (has the Arkham-style combat) and Middle-Earth: Shadow of Mordor/War games (AC-like and also has Arkham-like combat).
Definitely worth $4, even if you just buzz around here and there for around for 4-10 hours or so.