Great choice. A moderate in a way that, in some respects, even Koizumi wasn't. Not a big fan of the Yasukuni shrine visiting, not enormously hawkish, and just in general a stabilizing influence that'll be a nice change from the Abe/Aso crew.
He's also facing a very difficult situation, though, as he's not so dovish as to oppose the Afghan mission refueling that Japan signed up for. With the possible revelation that Japan has been refueling vessels going to Iraq, instead of Afghanistan, the opposition DPJ may well step up their opposition to the refueling program.