The old Doom games were ones I would play over and over and over again. I loved them and I was even able to make my own levels! I turned out to be pretty good at that (I had a lot of time on my hands back then). I would still play it now if my laptop could handle proper backwards compatibility.
Then Doom 3 came out, which I absolutely LOVED. I had to drag myself away from the computer back in 2004 when I was playing it. I really loved it and I've played it about 10 times so far. Some people have said it's too dark and predictable, and I agree...but for some reason that game overshadowed Half-Life 2 completely for me.