Firstly I'd like to point out that If you've seen either of Mamoru Oshii's films, Ghost in the Shell and Ghost in the Shell 2: Innocence dont expect any continuity with these films as the Stand Alone Complex interpretation of the Ghost in the Shell universe is closer to the original manga in spirit. Also dont expect this to be on same kind of level as Oshiis films.
Thats not to say that Solid State Society isnt good, but its more like a feature length episode of SAC than a separate film. For this reason I would recommend watching both the 1st and 2nd Gig's of SAC prior to this as these are referred to in the film.
The only reason I havent given SAC 5 stars, is as mentioned above, it is more like a feature length episode, the quality of animation and cinematography are not wildly different than that seen in the anime, personally I feel they should have given it a little extra imapact.
I wont spoil the plot, but suffice to say ALL the main characters appear in this.