They do a lot of optimization for modern hardware like supporting wide screen resolutions. They fixed game ruining bugs and added a lot of mod like options in the settings.

For example it’s a turn based game so your guys do everything based on “time units”. In the base game it can be a big risk to peek around a corner, see an enemy and not have time to fire or even retreat back to safety. OpenXcom can show you how many time units you’ll have left and in colors if you have enough time to shoot when you get there. Cool stuff!

The AI seems pretty true to vanilla but they put in a rule that you have at least one turn to get out of your drop ship without being fragged or rocketed by aliens. There are third party mods that make the aliens work as a group to sneak up or flank you. Those scare me so I haven’t tried it yet lol