I have played through the game a few times on medium and challenging. Now I am going on realistic, and I have made it to Rebellion. It is incredibly fun on this difficulty.

I have heard there are other differences besides damage related stuff on realistic. Does anyone know what else changes? Thanks.

You cannot use Rambo tactics, Mercs have deadly aim and the AI is at its best. Try to kill as many as possible from long range. Use rocks to cause misdirection when you are not yet discovered. Headshots are a must.
Good luck

I have definitely noticed those things. I wasn't sure if the AI was different, but the soldiers clearly seem smarter on Realistic.

I just go through Archives last night, so things are going pretty well. There are areas on Dam and Volcano that I have no idea what I am going to do, but it will be fun trying new things.

When I made the campaign in realistic difficulty in video, I found really hot :
- the warehouse in Archive level, I think I died a dozen of times before finishing the map, first I was going too fast and the special forces were killing me, so I had to go more carefully ;
- the beginning of Volcano, in the hall, actually if you don't use rockets and nades you can't survive — I died 7-8 times before succeeding.

You can see my videos here :
http://forums.ubi.com/eve/forums/a/tpc/f/987108203/m/8751019065

I did it. I just beat the game on realistic. The final couple levels were pretty amazing.