RISK. It's a board game. Very fun with 3-5 buddies.
...oh wait, you meant video games. Um...hm.
Older stuff: Might and Magic 6 and 7, Caesar3, Lords of the Realm2. And some of others ppl already mentioned.
Newer stuff: Kotor1/2. FNV. That's it. Lots of newer games have been great fun and I liked them immensely, but I still wouldn't consider them "musts" for all.
Finally! I've been waiting for someone to post KOTOR.
I'm also really glad Fallout has received the love I failed to give it.
Keep em coming I've got some great suggestions!! If I get really, REALLY bored at work (impossible, but who knows) I might even summarize this all into a big ole list. After all, that was the entire reason I made this topic.
Thanks for posting
http://www.gamesas.com/user/601413-cactus216/, http://www.gamesas.com/user/530509-erginho/, http://www.gamesas.com/user/762133-agrona/, http://www.gamesas.com/user/709375-narmy/, http://www.gamesas.com/user/614140-intact-garden-gnome/, http://www.gamesas.com/user/93574-wingus/, http://www.gamesas.com/user/615553-colonel-martyr/, http://www.gamesas.com/user/661491-tommy-bozzer/, http://www.gamesas.com/user/701993-the-lobotomite/, http://www.gamesas.com/user/647883-ratslayer/, http://www.gamesas.com/user/715671-chef-kronus/, http://www.gamesas.com/user/552820-venq/, http://www.gamesas.com/user/637143-shifty/, http://www.gamesas.com/user/675697-sheogorath88/ (that website in your sig is aweseome!!), http://www.gamesas.com/user/749596-sheridanr/, http://www.gamesas.com/user/760850-gnrfan/, http://www.gamesas.com/user/395524-tinyhowie/, http://www.gamesas.com/user/314166-shoestring/ and http://www.gamesas.com/user/708894-shadow-stealer/
Great contributions!!