Finished my Dying Light repeat the other day. it holds up really well. I never actually played many zombie games, but my impression is it was one of the best ones. The story is slop (high production value but creatively bankrupt and soulless, a ripoff of better stories) but the gameplay is like crack.
You've got Not-Istanbul with a fast-zombie outbreak. Or, rather, the kind of zombies where some are slow, some are fast, some are big brutes, some are ranged, etc. Very video gamey. The central gimmick of it is parkour and a melee focus, and it works extremely well. The game could just as easily be an FPS Assassin's Creed game (especially in the historic district). Once you've gotten used to it you can fly around the map in seamless motion.
It doesn't make great use of its other gimmick of the day-night cycle, though. Night is way harder, to the point of essentially flipping it into a game of stealth and flight (moreso the latter, you can't practically stealth except for one extremely cheesy* camoflauge ability), but it wants you to rescue packages for much more points. It's meant to be a stressful, scary challenge. You can come to find that the way to do it is to set up your chain of outposts in the daytime (so that you don't have to survive crossing the map, but leapfrogging). Early on the balance is a lot harder, but later on it both takes away the packages (and thus the main rationale for going out at night) and makes everything a little too easy. I think the intention is maybe that you switch to actively hunting the stalker monsters at night, but I never really did that. They're extremely strong to the very end and it never makes you learn how to deal with them.
The map is really, really impressive on top of the movement system being so great, and it's fantastic how many interiors it has for you to play in (for quests).
*You can become invisible to the zombies by smearing their guts on you then, with another ability, just kill them one by one in the state, using each new body to top off your camo. It's one of those things you have to force yourself to NOT do. Could have been balanced by having stealth kills not allow you to camo up, or blow your cover.