Some episodes just seem to punch you in the guts. This, despite the total lack of action, is one of them. The first 5 seconds set the tone: disturbingly familiar, chillingly realistic, and yet deeply touching and so well interpreted that despite every horrible reminiscence it might conjure up, you probably won't drop it before the last minute. I know I never do even though it physically *hurts* to watch. Yup. Every single time.
Fortunately, the whole episode is brilliantly balanced on the fine line between comedy and nightmare, mostly thanks to the cast's really great performances. Nobody overdoes it, conveying just the right blend of emotion and bravado. Every little detail feels right and says something about how the characters interact and how they truly feel. Obviously, most of this revolves about Rodney. His intelligence is everything to him; losing it, and seeing himself losing it, has to be the most horrible thing he could imagine --and yet it provides such wonderful moments, adding a new depth to his relationships with others, particularly with Sheppard and Jennifer. It's mostly thanks to those three that an episode without any particular significance for the season acquires such resonance.
Last but definitely not least, despite what you might think from reading this, the episode actually has several honestly funny moments to offer, and it manages to blend them seamlessly with the ongoing tragedy. Of course, another thing that rescues the episode from the brink of depression is that obviously, for once there will be a cure. Wishful thinking it may be, but it's still comforting, and I think that this is one of SF's best points: not to look away from reality, but to look beyond it, if I may say so.