After careful consideration, I worked out that this is probably my favourite season of Stargate, which is why I bought it. If you're familiar with the programme, season 4 featured more:
high quality adventure (season opener "Small Victories," "Watergate," "Tangent" and season cliffhanger "Equinox" to name a few),
enjoyable comedies ("Window of Opportunity," "Upgrades" and "Point of No Return" are all hilarious),
high concept science fiction ("Beneath the Surface," "2001")
and very involved moral conflicts ("The Other Side" and "Scorched Earth"),
than any other season before or after it, as yet. The characters are also at their peak of humour and interaction, and there's also some attraction between O'Neill and Carter that is expanded this season. Daniel and Teal'c are also given many opportunities to shine.
As well as the superior episodes, all of which will make you laugh at some point amidst the action, the picture quality of this set is greater than seasons 1 to 3, simply because it is newer and Stargate was filmed with clearer lenses. The extras are also a greater bonus- each DVD has some aspect of Stargate behind the scenes talked about, and the interesting and often funny audio commentaries can make all the episodes enjoyable to watch even if you've watched time-loop extravaganza "Window of Opportunity" too many times.
Overall, this should be the essential purchase for big Stargate fans, before the show changed for the worse in the next couple of seasons. The box is a nice orange colour too.