I got 7 Days to Die the other day, and would personally say that it is something you would not regret if you enjoy both PZ and Minecraft already.
Playing by yourself, although rather lame, is a great way to get to know the gameplay and crafting recipes, as well as test out builds for bases and stuff. The only properly fun way to play is with some friends on a server though. Working together to build a base, defend that base, repair that base, gather and stash stuff...
As far as ridiculous numbers of zombies moving in hordes, it is one of the few games around currently that actually make it a bit of a challenge to fight hordes ranging in size from 3 to 300 zombies. The similarities to PZ are certainly there, in more than just a "they're both zombie survival games" manner, and the influence of Fallout and to a limited extent, Minecraft are easily recognised.
I would say it is still grossly unbalanced as far as gameplay, though it is not even in Beta yet - so by the 'proper' definition they are still adding content and functionality to the game (none of this "let's pre-release the indefinite beta to the public" bullshit that seems to be prolific among indie devs at the moment. A beta is not a release-worthy game). I'm surprised how complete it already feels though, most of the functionality of all the existing things is complete and bug-free, with the impending updates only containing more items, recipes, aggressors, and interactions. The multiplayer feels pretty much lag-free, and besides the ridiculous amounts of memory the game and dedicated servers can sometimes end up consuming, on a half-decent rig it all feels rather polished. Graphically, though it looks acceptably impressive and contains all the 'bells and whistles' effects and shading one might expect, there's something a bit off with the colour palette - After several hours of sustained gameplay quite a few people I've spoken with have found they develop a headache, perhaps due to the levels of contrast or sharply defined edges.
It's gonna have it's fanboys and haters, but if you're tired of waiting around for PZ to include NPCs, have enjoyed a bit of Minecraft in the past, or your gaming has taken a backseat during the long wait for some upcoming releases then I think you'll enjoy 7 Days to Die. All that said, the biggest downside for a lot of people here is probably the price. After seeing people claim that $8 for PZ (or however much it is now) is too much for an as yet unreleased game, the hefty $35 tag on 7 Days to Die Alpha is probably a turn-off.
