This is a magnificently produced game, and my second favourite video game of all time (Wolfenstein being my favourite game franchise of all time). It's such a shame that the game is not more readily available due to a licence dispute between Activision and Bethesda, and as such I'm extremely grateful that I still have my game disc.
The first thing that draws me in is the story. There are heavy ties to the five previous games, and despite Bethesda reportedly "turning their back" on this one, there are some big hints to it in future entries in the franchise. The cutscenes play out almost like a movie, which future games in the series would emulate.
Secondly, the game play. I'm a HUGE fan of the FPS, and this franchise has never failed to meet the FPS criteria with any of its games. From the range of available firearms and other weapons, to the different available upgrades, and even the accessible gatling guns around the maps, this is an FPS lover's dream.
And finally, the sub-plot. I'm talking, of course, about the supernatural elements of the game. I love the fact that the "Black Sun", the Thule Society, and the Nazi SS Paranormal Division are actually based on the existence of these things in real life (the last one previously referred to in Return To Castle Wolfenstein). Plus I love that they mixed this with finding secret rooms and passages from previous games.
I also love the open world aspect of the game: being able to wander around at your own leisure collecting gold and intel (like previous Wolfenstein games), and completing missions in your own time.
To be perfectly honest, if I had to fault one thing, it would be that they forgot to add the chicken dinners.