Most Underrated TOS Episode?

[Gaseous Anomaly]

All of the TOS episodes were under rated, if not it wouldn't have been canceled so quickly!

 

[tomalak301]

I just say Tomorrow is Yesterday last night. That's a very good episode, but I don't know how underrated it is.

 

[cooleddie74]

^
Actually, it ranks pretty high on most fans' and critics' lists. One of the few TOS episodes to get a 9 or 10 on the ex-astris-scientia episode guide/review pages.