DISCLAIMER: I have spent only two hours in this game at the time of writing this review, and have not played the original.
That out of the way, and having played many games similar to this over the years I feel I can at leaast provide a balanced review at this stage, amending and adding to it as more content is inserted and the game is refined.
When I booted the game, and immediatly went to Options, as I do, the first thing I realised was that some of the Control headings are left-overs from the original (soon to be amended). As it stands, Gadget does not mean what you might think, but actually means "Focus Fire" and Melee actually means "Use Gadget". Confusing when playing the tutorial if you re-mapped the keys and forgot what the defaults were. Anyway, something that will be fixed.
To the game itself. My first impression was positive, immediatly bringing to mind such similar titles as "Breach & Clear: Deadline", where you are fighting off the infected/zombies and "Door Kickers", another top-down CQB strategy title that is made up of missions, not a campaign. Oddly enough "Atom Zombie Smashers" sprang to mind immmeditaly as well, and if you've played that little gem you'd see why. However, whereas "B&C:D" and "DK" focus on realistic weaponry, stats and contain strong RPG elements, this is more abstract and 'comical' with the focus firmly shifted more toward puzzle-solving than pure strategy (probably where "AZS" fits in). "SS:G" is not just a light strategy title then, but a sometimes quite complex puzzle game where you might spend up to ten frustrated minutes in PAUSE mode trying to figure out just what you are supposed to do on only one part of what could be a huge gauntlet.
So, you have from one, two or four survivors in each "gauntlet" (mission, in other words) starting with an infiltration point and a FoW obscured map, lit only a short distance by each unit's facing radius. You'll battle your way through rooms and corridors until you find your objective, dodging a veritable horde of infected with tlents you'll be accustomed to from "L4D2" - spitters, jumpers etc. So, you survived many attacks and explored say 4 rooms up to this point (opening crates, picking up newer weapons), and are ten minutes into the gauntlet/mission (explored rooms are faintly visible so you don't need to return). Here's where the gam,e gets interesting and the difficulty rises, sometimes unintentionally. For one gauntelt it might be to find three items to open a door, each one in a different direction (north, south, east etc.). So, go south young man/woman....only it isn't a room or two you need to discpover. As you travel down that southerly corridor many rooms will presetn themselves wityh sometimes several different ways to enter them requiring the puzzle solving I mentioned. Buttons must be poressed together, or sensor plates stood on in a sequence. There is the "Aha" moment when you discover how to get into a room or corridor only to find there are so much firther to go and so many obastacles. What appears at first to be a simple, short'ish mission has now become a labarythine nightmare where you cannot save the game, but only pause (where eerything goes very, very dark. A SAVE game point, either manual or auto would be much appreciated, particualrly if you are a casual gamer or, like many you'd like to redo a stage, not start from the beginning, some 45 minutes back.
That's the game. Add to this a robust and fully implemented editor where you can create your own gauntlets and upload them, something that will require hours of work believe me and that is the package. There are already loads of developer created gauntlets to come to grips with, and a tab for user-created gauntlets when tney become available.
Who will this appeal to? Not, as it stands the casual gamer in the long term, at least not without Save points or manual save. For the price though, if you enjoy squad-based strategy CQB's with puzzle solving elements you'll be right at home here. Frankly, you'll have a ball.
Is it worth it if you own the original? I can't say. There is no campaign as such, but the promise of user generated content and the healthy amount already on display, then if you're a fan you might want to have a look.
The Dev is continually updating the game, refining and patching weekly, listens keenly to the community and responds - something many other Devs (even Indie Devs) could take a leaf from.
I know I'll be going back for more as each time I start the game I find something new to stretch my grey matter. This is one of those titles that can easily slip past your radar, and that would be a shame. If you do enjoy what I've described then do yourselves a favour - buy it and have a ball!