It's a atypical psychotic and a rather potent one at that. It has much more potent anti-psychotic activity then say Quetiapine or olanzapine and is a much stronger D2 antagonist then either of these drugs.
I don't find it great for treating my bipolar disorder on it's own but taken with lamotrigine and bupropion it does help. Not as good as olanzapine though atleast for me. It also has more side effects then olanzapine or Quetiapine and since my insurance only covers risperidone and quetiapine i have been on quetiapine lately because it gives me less side effects in general compared to risperidone.
It can be used for bipolar disorder either as a monotherapy or as a add on to a mood stabilizer or anti-manic drug such as Lithium, lamotrigine or divalproex. It is also given alot with a anti-depressant such as bupropion to treat bipolar as well. It can cause depression in some people because of it's rather potent dopamine and serotonin antagonism so it won't usually help the depressive side of bipolar disorder.