What are the difficulties of landing on an upslope runway?
As far as landing in a up-sloped runway is considered, the pilot will make a lower approach if not careful as he/she may consider the ground before to be sloping up as well. From flytime.ca:


  When a runway is upsloping, the pilot thinks that the runway continues on an upslope from the terrain before it, hence thinking the terrain in front of the runway is upsloping as well.   The pilot will judge their altitude as too high, because they perceive the terrain continues on an upsloping, positive angle towards the runway  and will consequently plan a low approach that can cause landing short of the runway.




Image from flytime.ca

Another thing to note is that the landing roll will be reduced (on the other hand takeoff roll would be increased, if takeoff is on uphill direction; else, it's reduced). For example, in this airport, the actual landing point is level- shortly after the aircraft touches down, it will start traveling uphill, and the landing roll will be shorter. One (passenger) describes the landing as:


  During the approach we were below the runway and climbed up to it to land. After touchdown, we slowed down very fast due to the upslope. Very different than the normal runout after a landing. 


Of course the location of this particular runway means that the landing has to be done correctly the first time around.