I havent had Gilbert but people from year above said he is really good. He challenges you to push yourself. However, that said, a lot of first years find that very difficult and struggle to get through the semester. I probably wouldn't recommend him if you want to slowly transition into law school.
I haven't heard about Brown/Atherton. I think they are fairly new lecturers to UNSW.
For Lixinski I havent heard much about him but you can have a read about him here
http://www.law.unsw.edu.au/profile/lucas-lixinski
Fitzsimmons I heard mixed things. Some people enjoyed him some didn't. From what I heard he doesn't teach the course so much to say but rather facilitate the class to do discussions.
Hope that helps. Sorry couldn't be much of a help.