Is surprisingly good. The lack of review copies before the day before launch sketched me out a bit, but I'm really enjoying it so far. The day/night cycle really enhances things, human enemies are much smarter than their zombie counterparts, & guns attract crazy amounts of attention. I already enjoyed the melee mechanics in Dead Island (I have Riptide from a steam sale but never played it) & the parkour adds a constant amount of intensiveness (think Farcry 3/4's tower climbs, just ALL the time).
The open world sandbox really allows you to approach situations in creative ways, so that's neat too.
I'm only about 10 hours in, but I'm very much enjoying it.