Interesting how almost all the shows mentioned are fairly recent.

For a lot of people it's probably because they're young and don't remember a lot of older shows. I'm old enough to remember TV from several decades, but for a lot of my favorite shows from the 70's (for example) I don't know which episode was their first, or their first episode wasn't that special.

Twin Peaks

ER - without a doubt. Totally rocked the tv world.

Personally, I loved loved loved the pilot episode of Alias. One of the best things I've ever seen on tv. Unfortunately, it's been a pretty average show since then.

Roswell
South Park

Alias was a really good one... Saw the first ep (aired commercial free) & was totally hooked.

I'd also toss in the Family Guy. I don't know if it was all the beer we drank during the Super Bowl, but when the Kool Aid Man broke through the way, everyone in the room just lost it...

I don't remember, but I think Sliders had a good first episode.