Currently Online 
OK, this is another really difficult year. I love Descent. As you said, the progenitor game of the 6 Degrees of Freedom genre and a great game in itself.
https://www.youtube.com/watch?v=SuMBYZrcQfU
But I also love Star Wars: Dark Forces, which is probably my most beloved FPS of all time. Another LucasArts game, which were really gaming masters back in the day.
https://www.youtube.com/watch?v=hgF9-C-hsL4
When we have games you forgot to list. Like Jagged Alliance. There was a third entry this year by the way. But I still love the original. It is turn-based strategy, but each mercenary has gotten a strong personality... very strong. Some dislike each other so much, they might shoot at each other instead of the enemy. So you should really read the file on each hire.
https://www.youtube.com/watch?v=4Acro82SEdI
And finally we have the first entry in the Worms series. Again this is like Scorched Earth, but adds some quirky character in form of the worms.
https://www.youtube.com/watch?v=E5o4ReqhcaY
Really hard choice, I love all four games. I go with Jagged Alliance here, because it is an outrage you didn't even list it.
