Bought my copy of the 15th Anniversary quite awhile ago and I believe it came with a slipcover, now that it is heavily discounted I don't know if that is still the case though.
Stargate - Extended edition only, mediocre picture quality, just a commentary track
Stargate: 15th - theatrical and extended cut, much improved picture and sound, commentary, pip-mode, 40 minutes of featurettes, and a gag reel