I liked the early seasons (1-3) where they actually went through the gate every week, had scary believable enemies in the Goa'uld, a sense of wonder with multiple mythology arcs, fascinating human offshoots from past cultures, an intriguing earth side conspiracy plot and not lets rip off the X-Files, and didn't have deux ex machina technology fall from the sky when the plot needed it (or get rid of allies when the plot needed it, like the Tollan and Martouf). Admittedly season 1 had its cringe-worthy moments, but the show got it together faster than most. A thread from an obscure reference in a stand alone episode could be picked up one or two years later and prove to be a key moment in the series.
I feel the series went downhill when Glassner and most of the other original writers left and were replaced by Mallozzi and Mullie (though Brad Wright and Robert Cooper have delivered very good episodes since too, and did a great job on Atlantis season 1). For me, SG-1 became a very different series very quickly and went from being my favorite show to one I just watched.
After season 3, my favorite season was season 6 due to them rediscovering some of the series' roots and actually exploring again in a couple stand-alone episodes.
I should mention I've been an SG-1 fan since its second season aired. I think SG-1 is unique among genre shows it that it didn't peak in its popularity (at least in the US) till it moved to the Sci-Fi channel and gained a mass audience verses a small tight fanbase early on when it was on Showtime and syndicated at 1 am on Fox affiliates. Therefore each season will have its own fans based on when they joined the series in progress.
Seasons 1-3: Original SG-1
Seasons 4-5: Later Showtime, that led Michael Shanks to leave the show
Seasons 6-7: New lease on life on Sci-Fi
Season 8: the real last season
Season 9-10: Stargate: Command
Stargate's strength may be in its ability to continually re-invent itself. I just wish more stand-alone episodes post season 3 had continued with the show's original themes and Mallozzi and Mullie didn't write a third of each season's episodes.