The second and third shots of Michael Shanks as 'Daniel Jackson' shown in the opening credits (one where he runs into a scene that has the Stargate in the background with a closed iris, and the other a closeup taken from a low angle as he studies something out of view) are both taken from this episode.
The trivia item below may give away important plot points.
This ep (teleplay by Bobby Cooper, later producer) is loaded with plot points for later eps. It marks the first time the following major points are referred to: 1. alternate/parallel universes; 2. 38 min time limit for keeping the gate open; 3. Mention/use of a Beta site; 4. parallel universes with different team members of SG-1; 5. Teal'c deciding to leave SG-1; 6. Alternate Sam with long hair; 7. SG-1 travel aboard Gou'ald space ship; 8. first time to show interior of gou'ald space ship; 9. first time to show stargate operating on spaceship; 10. first to show a mechanism to control spaceship (although changed in other ships); 11. first to show death gliders; 12. first to show planetary invasion using gou'ald ships; 13. first to reference Sam speeding up dialing process for Earth gate; 14. first to reference self destruct in response to gou'ald invasion; 15. first time to show Daniel Jackson looking himself up in alternate dimension/time-line; 16. first time to show SG-1 risking courts martial and disobeying a direct order; 17. first to show gou'ald two-way communication sphere; and 18. first to make explicit reference to Sam and Jack's romance, even if only in alternate dimension. There are undoubtedly others.