It's pretty obvious that Gordon is on good terms with most of the guards in Sector C. Even if he goofs around and slacks off despite being needed down in the test chamber, the guards will do nothing more than smirk at his antics and say they'll go get a beer after Gordon clocks out. In the cafeteria you can find one guard nursing a cup of coffee and talking about him putting in overtime. Gordon seems to sympathise with him, as we get a genuine smile and a 'cheers' in return.
Fighting to keep Guards and Scientists alive. Due to improved AI, better voice acting, and variable appearance, they feel a whole lot more like people than they did back in Half-Life 1 and because of that you will feel much more inclined to keep them alive. And you just generally feel pretty awesome when you do.