YouTube has an alternate opening for Where No Man Has Gone Before in sort of a Quinn Martin style. Disregaring the Quinn Martin aspect, I think this opening is more effective.
It starts with a picture of a galaxy that is supposed to be our own and has a voiceover by Kirk. He talks about how everything they have known will be a speck and that they are heading into the black void beyond. I think this gives more of the feeling of being out in space and would have made the episode more effective.
The voice over stating that until now their mission had been one of space law regulation is a non-starter. This was one of Roddenberry's early ideas that was eventually scrapped (thankfully), but not before this voice over was done. I have an audiobook introduced by Shatner where he talks about Roddenberry's idea on this and he says something like "Commerce regulation....we didn't even have pockets." Anyway, he says that they are now a probe going to where no man has gone before. This makes the revelation of a signal from a ship missing for 200 years far more effective.
I also noted that Shatner is the only star listed in the opening credit before the commercial break. When they come back, Nimoy is listed as a co-star. But I digress.
The shot of Gary in the Mitchell sort of lusting after the hot yoeman gives a lot of depth of understanding into Mitchell's character that is only hinted at in the final aired version. One could see him and a younger Kirk womanizing together.
The scenes of the corridors that were cut out also increase the feeling that this is a ship, and not a set.
The Quinn Martin "Tonight's episode" etc. stamps do not really contribute anything. I'm glad they dropped those.
Anyway, my humble opinion is that overall, this would have made a more effective opening to the episode, and for the series overall.
This is listed on YouTube as "STAR TREK UNAIRED VERSION 2ND PILOT INTRO from 16mm film". http://youtu.be/GFtc2Ypwzl0