I own this game on the Switch, and didn't use GoG for it. As far as I know, there's no difference between the versions. I don't like spoilers, so I will try to not mess with you by giving any of those. The TL;DR : This game is worth it. If you want a good Metroidvania experience, this is a game you want. A list of other Metroidvanias that I think are great, so you can compare: Axiom Verge A Robot Named Fight Vision Soft Reset Iconoclasts The Messenger Super Metroid (+ the other 16-bit Metroids)
The main flaw: Glitches. Although there is a patch to fix this, items still do not always work properly. I have reached a point that cannot be progressed past, despite having the correct answer to the puzzle. (I looked up multiple walkthroughs online to make sure that the solution was correct.) The patch is supposed to prevent this sort of problem, from what I hear. But even those walkthroughs admit that the patch does not always work. So for me, there's a 2-star review.
Those trailers make it look like you'll be playing this wonderfully minimalist game, where you get to focus on the pretty environment, well-crafted monsters, and really just focus on the crawl and its puzzles. This is not the case. During combat you will primarily be looking at the bottom-right corner waiting for weapons to come off their re-use timer so you can click them. Magic is very slow and clunky. The combat system is very, very bad. You can't really look at the enemies while you fight, you just look at the bottom-right of the screen. Also, combat mechanics are very counter-intuitive or even deceptive (for instance, ranged combat never misses, no matter your Agility score, so a low dex Minotaur is the best archer). The vast majority of the puzzles are really just timing 'puzzles,' so you HAVE to turn down your graphics in many case to be able to make it in time. This defeats the one redeeming feature of the game: the graphics. This was a great idea that needed a great deal more refinement before it looks as awesome as the trailer. I look forward to the next game they make to see if they fix any or all of these major problems. But as it is, I am really not a fan. I want to look at my games while I play them, and I want my RPG puzzles to be RPG-y, not action-based timing where I have to turn down my settings (I have a 2 GB vram video card if that's any indication -- GeForce GT 420).
This is interactive storytelling brilliance. This may be the best story-driven game I've ever seen; one sm all plot device (the machine), and you have an incredible story. And the soundtrack is perfect for it.
