I have seen a few reviews of the game and consider buying it, since it is on a sale.
But I need to know a few things and I hope that the members of the community will help me out.
1. Does the game still get updates (on GoG or somewhere else) or is this the final product?
2. Is the game in its current state playable?
3. Is/has been the developer responsible towards the game and have they kept attention to the community's needs?
One bonus question:
4. How heavy is the game, in relation to mechanics? Is it difficult to get into (something like Dwarf Fortress where you have to watch hours of videos and read dozens of pages of documentation to learn) or is it a simpler experience?
Thanks to anyone who might decide to answer the questions.
To answer your questions:
1. No, it's been complete for quite some time. Gog is fully up to date, we're not behind patches or anything.
2. As far as I am aware, there are no bugs in the game as it now stands - at least none that I have seen or heard about. It's possible to play through and complete in a number of ways.
3. The dev has changed some things, early on - mainly bug fixes from what I can gather. It could be argued that there's room for quality of life changes, but that would likely require a redesign (the UI can be somewhat clunky, but that partially stems from the fact that it's possible to rearrange your inventory. There is an auto-arrange button which works fine for the most part though. It's also clunky because of the significant flexibility of the crafting system - in general, if an object can function as a stick, it can be used in crafting recipes requiring a stick).
4. The game is pretty damn brutal. I didn't bother with gameplay videos, because I hate watching other people play things and that takes too long, but it's definitely worth heading to the game's website, forum and/or guides to get some survival tips if you find yourself getting frustrated. That said, dying many times is one of the game's charms - you're not a hero in this game, as even if you create a combat-focused character, you could still get wiped out by a guy with a gun if they manage to shoot you in the head. There are ways to mitigate danger of course - which usually boils down to "don't fight something more powerful than you unless you're well prepared" - and even then you might still get killed.
It is most definitely a brutal game, and you will almost certainly die many times before you "complete" it. But making it through to the end isn't really the fun - it's all the stuff that happens on the way. You can easily ignore the plot forever if you just want to hunt in the wilderness, for example.
Finally, you didn't ask this, but know that the game is moddable (one of the things added by the dev after request), and there are a number of mods around, most of which change the crafting (in theory, you could invent entirely new objects, and invent crafting recipes for those objects (as well as for anything else in the game)) - in addition to creating new plot elements (though not sure if anyone's actually done the latter yet).
I'd recommend it even if it wasn't on sale, despite the fact that I've only ever "completed" the game a single time out of god knows how many runs (although I often play as half-blind insomniac weakling, which probably doesn't help).
One of the awesome/hilarious/evil things the game does, is that it starts you off in one of the most dangerous parts of the map. Most people (including me) tended to hang out near where you start, since a number of things point to that making sense. If you get this, take my advice, and don't do that - get the hell out of there to somewhere less full of the toughest enemies in the game (before the first day ends, you should get a big hint of a good direction to head in).