Just to let you know numatrix, it's generally frowned on to resurrect old threads unless you have new stuff to add but I'm glad you did. 
This is one of my favorite episodes of TOS. It's odd that I like it so much because I'm normally very turned off by gross scientific absurdities and ludicrous plots - and this episode is King in that area. Spock's Brain, TNG-Masks, VOY-Threshold have nothing on this episode for absolute lunacy. But The Immunity Syndrome holds my rapt attention from start to finish. It's got plenty of drama, it has great character moments and probably the best special effects of the series. All you really need to do to eliminate all the problems with this episode is replace the ludicrous amoeba with a TNG-style quantum spatial anomaly or some such thing. I think if they had done that, this would be considered one of the best episodes of the entire franchise.

This is one of my favorite episodes of TOS. It's odd that I like it so much because I'm normally very turned off by gross scientific absurdities and ludicrous plots - and this episode is King in that area. Spock's Brain, TNG-Masks, VOY-Threshold have nothing on this episode for absolute lunacy. But The Immunity Syndrome holds my rapt attention from start to finish. It's got plenty of drama, it has great character moments and probably the best special effects of the series. All you really need to do to eliminate all the problems with this episode is replace the ludicrous amoeba with a TNG-style quantum spatial anomaly or some such thing. I think if they had done that, this would be considered one of the best episodes of the entire franchise.