The long time given to make your move is a big problem on party poker IMO. Even 4 tables gets incredibly boring especially as you run dry. Comparing to 4 tabling on the Prima poker rooms I would say that at least 6 tables on party would give me as much to do as 4 on Prima.
Its in fact so bad that I once saw someone making his every move in the last second just to annoy, the table became slow enough to make everyone leave within 10-20 mins.
I say cut the time given to make a move to half of what it is!