Guy Williams and Mark Goddard put in EXCEPTIONAL performances as their evil counterparts.
The anti-world costuming is great and is a refreshing change from those horrid pastel Easter marshmallow peeps colors, as are the sets. Even care was put into the anti-world Robot prop.
But consider these:
Anti-matter John Robinson says they've been waiting for a window for thousands of years. If they are in a parallel dimension, the time term used is ludicrous.
A scene reveals a scar going all around Anmtimatter John Robinson's head. WHY? While it evokes horror, it is left unexplained. Was it an attempt to do too much with the storyline? Or mindless horror, haphazardly thrown in?
These drawbacks alone throw spanners into what could otherwise be the finest episode ever - and don't get me wrong, I would be compelled to say this is the best episode ever anyway. In terms of content, potential, and an average episode of how the series works too.