First proper play racking up two hours, the verdict: excellent base to grow from and once reduced to 16 x 12 for 4:3 res it runs as quickly as any other Source game on an old PC, any Intel machine wouldn't break a sweat if you had 8Gb RAM. The park level is deliberately claustrophobic until you reach the central "pond" area, where you can get 10-15 attacking in one go, so in SP where you have all the ammo to yourself you can learn the maps and live long enough to properly explore.
Having to aim properly in a Zombie game is strange
but rewarding, you can channel your innner Walking Dead TV Show and take them down one at a time. Unlike ZPS you can carry around other ammo without slowing down. On the Roanoake PD and Aurora Estates levels you get a lot more "Velociraptor" zombies that scale the fences and attack from the side whilst you're aiming at the Z you saw in front of you, right now that all adds to the challenge and you can take damage in multiples of 10 until you find a medkit. In the non-Hunted modes I'm pretty sure Infection would be another game element from the "lead" Zombie, I will have to try extraction in a proper server but I'm happy the game's been worth the wait.