Almost always I can tell if a game is for me or not within the first four hours and I'll just return it on Steam if it isn't. I've done it dozens and dozens of times without any problems.
Now, sometimes I'll not be entirely sure if those four hours are enough but some reviews left me unsure. Star field was such a case. I procured that through alternative channels and decided after about twenty hours and four times as many crashes that it was indeed shit.