I agree, pretty much just watch these episodes, there might be a random decent episode in the beginning of season 3, but I doubt it.
The one I would add is the season three episode "Double Cross"; it was meant to be the season three premiere, but ended up being aired second. "Double Cross" is a good episode with some unique angles of sliding to add, and it gives a taste of how things visually changed in season three.
There are things I like about the rest of the series, but it never lived up to season one. The show lost something when Robert K. Weiss backed off in season two; and I think John Landis and Leslie Belzberg leaving after season one had some effect to. The comedy element suffered, and I think that was an important part of the Sliders mix.
In all, I still love the series; I accept it even with its flaws. However, I agree that season one and two are what people need to watch. Watching the rest may just break your heart.