You might want to read the rather lengthy thread in the Faith Issues section, entitled "Will the EO and OO reunite."
If you want to get a succinct statement of the actual issues that need to be resolved, maybe someone with more patience can do that. It exhausts me to even think about it. Quite frankly, I personally believe that what is keeping us from having full official communion is a lot of pride and bigotry on the part of some people. Unofficially, some churches have already opened up communion to the people on the other side. For example, I don't know of an Armenian priest who wouldn't give communion to a Greek. Also, there is a Greek church about an hour away from my own which communes Armenians.
A good book for examining the issues dividing the two churches is The Council of Chalcedon Re-Examined
, by V.C. Samuel. You can find it on Amazon.com:http://www.amazon.com/exec/obidos/tg/detail/-/1401016448/qid=1125269612/sr=1-1/ref=sr_1_1/103-8465255-1147816?v=glance&s=books