I found this film a bit disappointing, though ultimatly enjoyable.
The problem is that you can't really understand the entire story line unless you watch it multiple times, and spot the various 'bodies' that the Major may be using throughout the film. And when you have worked this out, you have the final enigma of whether the superficial conclusion is actually what is meant (this is probably intentional, but ultimatly leaves you with the feeling of a lack of closure).
In many ways, the story expands on the question raised in the original 1995 film about identity and self, and as such is quite thought provoking. This is the basic theme behind the whole story ARC, and is also explored by the ultimately trajic Tachikoma story (in SAC) as well.
BTW. On the timeline business, SAC 1st and 2nd Gig must be set before the original film, bearing in mind what happens at the end of that film. Innocence follows the first film after a gap of many months, and SSS is over a year later than the original film. So it is axiomatic that Togusa is in GITS (and he is).
I don't really believe that the stories in the original film and SAC and SSS are incompatible with each other. I would definiltly suggest that you need to be familier with some of the other (or even all) of the films and series before embarking on this one.
The various GITS soundtracks are permanently loaded in my 'phone, and are probably listened to more than anything else in there. Brilliant writing, and the choice and quality of the artists is superb. Yoko Kanno (primary music for everything apart from the original film) needs more exposure outside of Japan and the Anime scene.