I've been a fan of this game since it came out, more so even than Medieval 2 and subsequent games in the series, and the only problem I had with my new Mac was the lack of games, specifically this game.
It's an excellent transfer from Windows to OSX, both games work pretty much flawlessly and it's as much fun as ever. Modding potential is limited simply because most of the modding community work on Windows (unsurprisingly) but Europa Barbarorum works well, and the website explains how to install it even if you have no previous experience in installing mods on a Mac (like me). The game did crash once when I was running EB and the music can get stuck during an EB battle, but that's not really part of the product anyway so don't base an opinion on that.
Added bonus - it arrived the morning after I ordered it, despite choosing standard delivery which could have taken up to 12 days. Whether this is standard for these guys I don't know, but I certainly have no complaints!