I cannot say enough good things about the premiere episode of Mission: Impossible. It set the stage for all the great elements of the series.
In particular, it really set the stage for the first season episodes that had a lot more raw violence and a lot more serious threats, e.g. WMD attacks on American soil.
You can find the opening montage for this episode on YouTube. There's so many very good episodes that it's hard to say if this one is the best. However, I do believe that this first episode had the best opening montage of all of the episodes. In particular, watch the last two clips in the montage, and how they are perfectly timed with the music. OUTSTANDING editing work.
Wally Cox was great even though he was cast against type. Fun fact...watch the episode frame-by-frame, and when Wally Cox's character gets his fingers crushed in the door, you can see Wally Cox holding a fake set of hands in the doorway.