In my opinion Doom is one of the greatest PC game ever.   It spawned sequels and many imitaions.   It started a whole first person shooter industry.   I personally enjoyed it more than Quake or Duke Nukem.  

1. Doom
   Simple and very fun.   Can run on 486 computers.   It would be very hard to find this for purchase anywhere.   My name is in the credits of the Super Nintendo Version (shown above.)  
   
   Network play but not playable on the internet.
   
   
2. Doom II
   An improvement on the original.
   
   Takes a long time to get through it.   I like the hidden Wolf 3D level.
   
   
   
3. Final Doom
   
   
   
   
4. Ultimate Doom
   
   
   
5. Doom 3
   
   
   
   
   

John Coffey