I am sort of on the fence about this episode. I was getting weird feelings about all of this before they even arrived back on Earth.
First of all, no way would they let Dr. McKay fiddle with this device under the circumstances. I don't care how smart he thinks he is or omnipotent he acts both Weir and Sheppard would have overridden his decision to take out the device and install it on the other Stargate when there was not a 100% chance of success. There was not a compelling enough reason to go with what they had to work with at this point. It would seem that the chances are they'll find another power source sometime to power the Stargate and then they'll send someone back.
The rest of the episode was sort of strange especially Sheppard's part. Weir did figure out sooner than later something was wrong. McKay didn't until he got into the science of the situation and found it was all drivel. Sheppard's reality with all the dead people had to be really surreal. It was interesting to see how they piggybacked Teyla's consciousness onto Sheppard's and she was along for the ride. Ford's was totally askew as they tried to reassign him?
Also if you look at the episode it was interesting how the characters acted differently in each set of stories. McKay acted differently with Ford then he did with Weir as it was their own versions of McKay they were interfacing with.
I liked the idea I think it failed in the execution somehow. Too many places for it to fail so I would start over from scratch. I enjoyed the acting and the settings so not a complete waste. Thanks for reading...