I'd say it was fine to skip the second film (Ghost in the Shell 2: Innocence), I remember it being a bit lacklustre in terms of the story and pacing. The first film is definitely worth a watch though.
I really enjoyed the second film when I first saw it. The scene with Batou invading the ship with augmented-reality map support was amazing.
I watched it recently though, and it just didn't really hold up. I'm not quite sure what it was. Maybe the ideas just weren't as innovative anymore? I think the first film stands up a lot better.