Kevin Martin is like Durant was before this year - volume scorer that does nothing to make his team better. Durant paid attention, worked his rear off - and is now a very nice defensive player. The Thunder are + with Durant on the court, they were big time - last year. Martin is still same old, same old - the Kings were losing 10 points per 100 possessions with him on the court compared to when he was not.
Talented like hell doing one thing only. Does not make his teams better one bit.
The Kings got much better. They have Evans who is much better than Martin playing his natural position with a real PG to help him handle the ball when he is not attacking. Just like what the Blazers do with Roy. Sure, he handles the ball a lot, and assists, but this way this is not his primary responsibility and he can concentrate on attacking while playing a secondary role as a creator.
The Rockets replaced T-Mac's unreliable production with Martin's unreliable production. They will be, however, much smarter and will use him a lot less with much less complaint when Yao comes back. T-Mac needed to be the man. Martin will be fine with reduced role - and they will be able to play Ariza and Battier when Martin does not work. Good trade for both teams, but at the end of the day - the Kings got much better.