Not my favorite defense here. On a real pick, I'd say if you haven't watched M*A*S*H you are missing out on something. Geek wise, Firefly.
Firefly all the bloody way. It took me years to get into it (after the movie premiered) but when I first watched it, I loved it. The world building was spectacular, Whedon is one of the best writers when it comes to managing multiple characters well, and you've got BIG DAMN HEROES! It changed the industry and, without it, maybe Whedon never would been given a chance to direct The Avengers. Think on that for a bit.
As for LOST...seriously, I don't care about that show even when everyone talked about it. Still don't know what happened, never been spoiled, and I will probably never care. No one talks about it at all. Firefly however everyone talks about it. Still.
(I'd still say M*A*S*H would be a better, non-geek pick though.)