I've been playing the original DOOM since late December, and used to edit it, although I don't edit anymore.
VERY fun game, nice background music, and a timeless classic.
I used to think DOOM really wasn't worth it, but when I played it, oh boy, did I think different. Absolute fun, strategy at perfect times (a.k.a. not constant thinking), speed, and still scary and keeps you on your toes.
I play it using DOSBox on Windows 7.