Wiping the memories of the entire cast is not a new thing in sci-fi. The most recent example I can recall is the episode of BTVS, also titled Tabula Rasa, where the gang didn't know who they were.
I liked that, finally, the expedition has run into a childhood illness that affects everyone on the base. Fic writers have been playing with the idea since day one, and it was never really done on SG-1 which is saying something considering there were upwards of 200 episodes in that series, but one would have to think that, along with potent alien punch and weird technology there would be something akin to the chicken pox on some other planet that would have an adverse reaction to the people from Earth.
The fact that everything became very militant was also very sci-fi. Alien plague breaks out, the infected are quaranteened, the military takes over. It's the premise of a hundred movies, not to mention more than a few tv series'. I liked the darker edge that Lorne had in this episode; he didn't have much to do this season, but the few episodes he did appear in he had fairly important parts in the storyline which is encouraging. I'm a big fan of Kavan Smith and I thought he did an excellent job playing a military leader who was not exactly the dry quippy Major Lorne we're used to.
Clueless Sheppard was a little strange, but panicked Rodney and take-charge Sam were perfect.
Anybody out there got a count on how many times Ronon's shot Sheppard now?