Whether you like season six as a whole depends on how much you enjoy Corin Nemec as Michael Shanks' temp.
Seasons seven and eight are SG-1 more or less as it was, except that O'Niell wasn't allowed to do episodes like Learning Curve or A Hundred Days anymore. Personally I don't see how anyone who enjoyed seasons 1-5 wouldn't enjoy this too, nor could I see how they wouldn't want to know how that overall storyline of the go'a'uld and replicators come out.
As said before, seasons nine and ten are really a different show. In one sense, the Ori are the go'a'uld taken more seriously (except that the general goofiness makes it hard to get "serious.") Whether you enjoy it depends very much I think on whether you like Ben Browder and Claudia Black, which I did. Especially Black.