Well I have been putting this off for a while because really I can't figure out how words can really express just how amazing of a show this is. I think I was 11 or 12 when the Pilot first aired. I didn't watch the show then because I was afraid of it after I saw episodes like "The Jersey Devil" and "Born Again" when they first aired, which is really funny because theses are some of the tamest episodes to me now. So unfortunately I wasn't quite ready or prepared for the X-Files during it's running. Later I remember watching TV one Saturday and there was a Chris Carter double feature. First "Jose Chung's From Outer Space" and then the Millennium episode "Jose Chung's Doomsday Defense". Both episodes had me in tears laughing at the dark humor.
I later found out that FX had an episode every night at 9 and so every night for an entire summer I got to watch an episode and I quickly became immersed in the mythology of the alien conspiracy. Some of the most memorable episodes for me from this period are "Bad Blood", "The Host", "Darkness Falls", "E.B.E", "Little Green Men", and countless others. I quickly became a fan but I had yet to see every episode and I avoided watching it new airings for fear of spoilers. So I began to buy the seasons on DVD. Over two years I was able to purchase and watch every episode. Interesting to me was the fact that I had already seen most of the episodes through syndication but there were many that I hadn't.
Anyway enough about my history with the show. The elements of the show that I think make it a great are simple. Likable characters, psychopathic bad guys, enough dark comedy mixed in with the horror and drama to give the viewer a healthy balance. The writer's of the show have a wonderful talent of leaving certain stories hanging only to the extent that does not make the viewer feel betrayed but wanting to watch more.
The X-Files defined an era of television and opened the way for other Sci-Fi related shows as well as helping define the crime drama shows that are all over the place now. If the 60's/70's gave us Trekkies for decades on, the 90's gave us the X-Files which will continue to create X-Philes for decades on in suit.