Overall I think the press conference went fairly well. Maybe that is because, in general, Bush press conferences are scary in terms of never knowing what he could say wrong and today there weren't any moments like that.
The initial opening statement was not nearly as good as it could have been. Maybe the quality of the speechwriters has gone down; there were a number of missed rhetorical opportunities that could have made the speech much more powerful. Although, it did get better towards the end of the statement, partly because Bush seemed to get warmed up and feel more comfortable.
One very good point in the statement was when he spoke about "the ideology of violence". That this ideology is the same in placing "roadside bombs outside Baghdad" as "blowing up children on a bus in Jerusalem", and thus connecting the global War on Terror to Israel's battle against Palestinian terrorists. Bush also spoke of the terrorists desire to kill Jews, specifically mentioning Daniel Pearl, perhaps the first time that a world leader is saying pointing out the anti-Semitism inherent in Muslim terrorism.
The actual question and answer part of the press conference was very mixed. Many of the questions were not very smart, and Bush did a decent job of avoiding the ones he did not want to answer. And there were a few questions that he was visibly struggling to answer or answered poorly. The question regarding the "false premises" of going to war is a perfect example of this. Others were answered perfectly; when asked if the American people deserve an apology from him like they got from Clarke, Bush answered simply and concisely that the "person responsible for the attacks was Osama bin Laden".
But what is more important and will be more memorable to people is the general theme that Bush spoke of, and that he did a very good job of highlighting, the future. Almost every question that was posed about past actions, he managed to turn into the goals and expectations of the future. This is a theme that will emerge more and more as a theme of the campaign; while Kerry speaks of past problems, Bush looks to the hopeful future.