First, I must say, awesome avatar and signature! Gotta love Alias.
Now, I too was sad to see Singer not directing this flick. I'm a huge X-Men fan and have followed the production since they got the writers a little over a year ago. I was worried that without Singer, we were going to get a Batman and Robin style film. Fortunately, they picked a director who is not trying to change the tone Singer set in the previous films but is keeping to that tone and also expanding on it. While Singer is a fantastic director I always felt he wasn't strong on the action front, this looks to be changed with Ratner as he has had experience in the action field while still able to pull emotional performances from the actors. What I find reassuring are the little references from the comics in this film, i.e. the Fastball Special and other fight sequences. All in all, the latest trailer shows this could possibly be the most action packed, yet most emotional film of the franchise.
Actually, it may not be the last movie with the "CURRENT" director. If there is an X4, I am sure they will sign Brett Ratner to direct again and he is up for it according to most of his interviews. Basically this is the last film of this current trilogy, or story arc. There will most likely be an X4 if X3 does well, but I am sure the line up will change which is a good thing to let other character's shine. I can see certain character's staying, i.e. Cyclops, Beast, Angel, Rogue, Iceman, Jean Grey (depending on what happens to her in X3) and maybe Storm. Wolverine on the other hand will have his own films so I think they will replace his character with someone similar such as Gambit.