Only my opinion, and I only had five days there, but I would recommend you visit the Citadela restaurant on the hill which gives magnificent views over Buda and Pest - it is ever so slightly expensive but the food is divine and the view is even better. Do the river cruise, visit the parliament buildings and the terror museum. Walk along the magnificent streets at leisure and visit the cafes to watch the world go by. I also went to see Honved play, got drunk with a Partick Thistle fan and visited a Scottish bar called (I think) The Caledonian, but you might want to skip that.