These are the elements i hold into account and base my purchase on:
1. General appeal (whether or not it's a genre i'm into, the settings interest me, the plot/characters interest me [depending whether or not it's story centric], whether or not the mechanics are stimulating)
2. Price (self explanatory)
3. Content quality and length (how well paced it is, design based on creativity, passion and not on trends, sellability, i don't like bloat and meaningless time wasting repetitive filler)
4. Replayability (ways to experience new content through subsequent playthroughs, multiplayer)
5. Mod-support (awesome)
1. and 2. being the factors that attracts my attention and warrants further research (user reviews and feedback [Steam, GOG, Reddit, Youtube, NeoGAF]), 3., 4., and 5. being the factors that fundamentally decide whether or not i take the plunge and get it to invest time into it. I have an extremely small amount of free time dedicated to video games (usually reserved on sundays), so i am incredibly picky on what i buy to invest that time in.