In Stars and Time is a weird game. The entire point of its time-looping premise means that, from a gameplay standpoint, you 'exhaust' the progression halfway through (give or take) and the games becomes more and more repetitive after that point (despite the options that become available to 'make things go faster'). I don't know if this is the best way the premise could've been executed, especially because if you have any interest in the optional content you'll need to repeat a lot of stuff a lot of time, which becomes tedious very fast; perhaps, more content being put into the combat for instance wouldn't have been unwelcome. However, I understand why the game was made with this structure and, thus, why it can be considered a 'by design' feature of sorts. Because it does service the story, and while that doesn't really make the issue any better, it makes sense in context.
And the story is where the game truly shines. Overall, the game is supported by an interesting world-building, albeit a lot of it is conveyed by text, that is also connected to its time-related incipit to a an extent. Thankfully, the writing is great and manages to hold everything together, and excels when it comes to the cast of main characters that move the story and, most likely, will be the main reason you'll want to push forward: all with very different traits, quirks, backgrounds, and problems that make them all memorable, and a lot of the major story beats are based on those characters and their interactions with each other.
I don't consider the game perfect in all aspects by any means, but I think that overall the final result is still something remarkable that deserves to be known by more people. And, if there's a chance that you may connect with one or more of the characters in a very specific way (confession: that's what happened to me), then the game may get dangerously close to a "one of the best games I've played" kind of deal. Despite this, keep in mind what I said in the first paragraph within this review and consider what you're getting before buying: it's a great time loop story, but it's also a time loop game with some undeniable quirks.
—oh, and if you're wondering about "START AGAIN: A Prologue" and its abscence from GOG, don't worry too much. In spite of its name, START AGAIN's relationship with the main game is complicated and it's hard to explain why without going into spoiler territory, let alone the fact that every player of both has their own opinion on the matter. For what it's worth, in my case I believe that In Stars and Time is its own beast that can be enjoyed on its own fully. Yes, there are connections with START AGAIN, things that go beyond its nature as a prototype, a demo-of-sorts of ISaT, but to me those are additional insights that are food for theorycrafting rather than an essential part of the main story. And gameplay-wise (yes, including what I said earlier) I believe playing ISaT blind has its own merits. So feel free to dive into ISaT on GOG (well, if you don't care about achievements at least :P), your enjoyment won't depend on whether you've played START AGAIN first.
