I only purchase full price games under one of 2 conditions. Either it's a series that I deeply love and know for certain will always put out quality games (Zelda, Mario, Monster Hunter) or it's a game that is extremely well reviewed and doesn't go on sale (factorio, other Nintendo games)

As for whether I believe a game I've purchased was worth it, I don't equate hours invested to price worthiness, but rather my overall enjoyment. I've put too many hours into games I regret ever buying (Ark) and played some games that were far too short but I would've paid double for (Outer Wilds). Rather, I believe it's how much the game affects you when you come out of it. Ark was a frustrating, grindy experience, but Outer Wilds literally changed who I am as a person. When I play something like Sonic Frontiers I come out in awe, and giddy with how much excitement that game gave me, but when I play something like Elder Scrolls Online, I don't dislike it but I don't feel anything special. Frontiers was absolutely a worthy purchase but ESO was not, because one really affected me and the other, even though I wouldn't call it a bad game, just didn't really do anything to me.