Serbia should leave Kosovo alone. Over the last several hundred years, Kosovo has been attacked and under siege by different groups multiple times. It is about time that Serbia stopped acting like a bully and let Kosovo take care of itself. Kosovo is filled with people who deserve the same human rights as everyone else and they will not get them if Serbia annexes Kosovo.
No, I don't think it's a good idea for one country to annex part of another. Whenever this happens, someone gets hurt. Someone gets the short end of the stick. Then people get angry, and desperate. They start a revolution of one sort or another. And war ensues. So no, annexation is not a good idea.
A very ugly war was fought over this issue and another war is not the answer. The people in Serbia, Kosovo and the rest of the Balkan states need to move forward and not fight more about splitting apart countries. They should focus on securing everyone's rights within their own countries rather than insisting that each ethnic group get a country of their own.
It seems like the government of Serbia is taking advantage of the massive amount of confusion in the region to press their political agenda forward. My guess is that it's just posturing in order to get a better deal from neighbors, but you never know how serious people in that part of the world are about their homelands.