This game is a bit of a mess that is carried by its co-op features and if it was only single player I would probably give it a 1.5/5. You get easily lost with the lack of map, there are frame rate, crashing and graphics issues that are far too common, and a lackluster weapon variety. The fact that only the host gets story progression and the guest can't see 95% of the loot ruins the experience and leads to one person being under-leveled unless you want to play two playthroughs.
If you think you would have fun taking down hard bosses with a friend in co-op then it's worth getting on sale, otherwise don't bother.