My main problem is that I'm not able to haggle with diplomatic deals like in RTW or M2TW. The AI says this is what you'll get (unacceptable deal for me) and you'll like it - or else (declare war next turn after I say no to the outrageous deal)!
The trick to that is giving a counter-offer. See if the AI decides to agree to something else, or just give them something outrageous so that THEY have to refuse. I never get DOW's.