I had great experiences with DayZ when it was still an Arma mod. The standalone was very disappointing. On the other hand, the dev of the original mod was the lead on the standalone (for a while) so buying it made me feel like I was contributing more directly to him.

Part of the reason I liked the mod so much was because of how unpolished it felt, the ui sort of stapled on top of the Arma ui, everything a little janky and you're plunged into a hostile zombie world. Funny how something unpolished can feel more appropriate.