twentysomething

Well, it's not my favorite, but pilot eps have to be watched, so, "Pilot." "The Man in the Fallout Shelter" is, ugh, it makes me cry every time I see it. Delights. "Two Bodies in the Lab" is necessary for a) Surprise!Adam Baldwin and b) FOREIGNER. (I'm also assuming you're not terribly worried about overarching things, like her parents, because that stuff is pretty Wiki-able, so I'm mostly going to for the squee/whump.) Those three will get you through s1, essentially.

I'm not a huge fan of s2, but it does have "The Woman in the Sand", which- UNDERCOVER VEGAS. (Although, "Judas on a Pole" is sort of interesting, but it's plotty? Eh. Also, it's directed by David Duchovny, so... lol.)

For s3: I recommend "The Mummy in the Maze" (HALLOWEEN. DORKY COSTUMES, JOY), "The Knight on the Grid" is plot-important, and a lot of fics were ep tags for this, but... eh. "The Santa in the Slush" IS CRITICAL. And loltacular, but SO MONEY.

I think s4 is super great, shipwise, in so many ways, so there are more eps from this than from the other seasons: "The Con Man in the Meth Lab" gives you Booth's brother in the form of Brendon Fehr, which, delicious. "Double Trouble in the Panhandle" is just-- UNDERCOVER CIRCUS, NO REALLY. "Mayhem on a Cross" is just- Sweets' backstory and a bonding moment that legit makes me tear up every time. "The Double Death of the Dearly Departed" is just an old-school hijinks ep that makes me laugh a lot. "The Critic in the Cabernet" and "The End in the Beginning" are SUPER SUPER IMPORTANT and really should be watched when you have time to watch them together (mostly, so you don't freak... although you will.)

And lastly, s5: "Harbingers in the Fountain" is pretty good, plus it's pretty essential for figuring out what happened in the cliffhanger in s4. "A Night at the Bones Museum" is hilarious and if you were an Ancient Egypt nerd like I was when I was a kid, it's SO GOOD. It's not a great ep, but "The X in the File" made me shriek at the tv, because I was like, "THEY'RE STEALING FROM MY BRAIN I'M WRITING THIS" And in retrospect, I think Hart Hanson had Dom Cobb Extract this from my brain, because it's all demon-filled. (I sort of felt that way about "The Witch in the Wardrobe," too.) "The Parts in the Sum of the Whole" is not only directed by David Boreanaz, but his dad even has a cameo in it- it's also an origin story for their first case, and Sweets makes the Sam Winchester face of WHY THE FUCK IS MY LIFE SO FUCKING HARD and I wanted to smish him forever. And then, naturally, the season finale, "The Beginning in the End."

So, that's about 16/17 must-watch eps, and a couple of discretionary ones- let me know if this helped!