If nostalgia it isn't a good enough reason to re-watch it then you should do what I did and listen to Kumail Nanjiani's new podcast, The X-Files Files. He and a guest (sometimes people like Dean Haglund!) discuss a curated list of episodes, plus look back into the early internet message boards and read commentary from the show's creators. Kumail Nanjiani is a hilarious and enthusiastic host, and listening to him nerd out with other super-fans is really fun. The podcast is still early in its run, just finishing up the first season, so it's easy to catch up.
And because we all love polls and arguing on the internet: what are your favorite episodes of the X-Files? I tended to prefer the stand-alone, monsters-of-the-week. My top 5 favorite episodes, in no particular order, are "Jose Chung's From Outer Space," "Humbug," "Post-Modern Prometheus," "Bad Blood," and "Unusual Suspects."
Please take this important poll and defend your vote in the comments.