I've been thinking about the GWB visit to Iraq, and found to my surprise that it was difficult to achieve clarity of opinion at first. But I've had some time t think on it and I think that the main thing that should be said about the surprise Thanksgiving visit is: well done.
There's a single reason why it deserves praise. Because for the troops in Iraq, it was an uplifting moment. Regardless of the soldiers' political or religious beliefs, hardships incurred from the long deployment, or problems awaiting them when they return, they are professionals and Bush's visit gave them their due.
Bush is a divisive, politicizing figure, so it's no surprise that his trip to Iraq is being spun hard by left and right. The conservatives see it in tones best described as "reverent-macho". The trip sets historical precedent, these are epic times, Bush is a fearless warrior. Etc.
There's no shortage of inane leftist commentary (see this comment thread at Calpundit for examples). But the conservative defenders of Bush's trip struggle mightily to paint legitimate critiques of the trip as identical to the craven loony bin. Tacitus for example pokes fun at Matthew Yglesias' complaint that no Democrats were invited - but notably doesn't address the more cogent points: that photo ops are nice, but good policy and leadership are better, and the President has no reserve of benefit of the doubt left given all the other craven political stunts he has pulled (including lying about the Mission Accomplished banner, and ridiculously transparent photographic maneuvering). Nor is the fact that the Bush visit was planned in October, but Hillary Clinton's Iraq trip was planned (and publicized) in September. It should be noted that Clinton's trip lasted significantly longer, including an overnight stay, and an actual visit to Baghdad rather than confined to the airport.
The President did a good thing for the troops. Extrapolating it to promote his personal virtue, or his vice, is nonsensical.
I take issue with the claim that Bush's trip is the first by a President to a war zone. I don't see why Bush's supporters feel the need to push this, because 1. it's irrelevant to why Bush's trip should be praised (unless you rank mythologizing Bush's courage as a higher goal than the troops' morale), and 2. it's completely false. Bill Clinton visited Kosovo four years ago in 1999, the former president Bush visited troops in Saudi Arabia prior to the first Gulf War on Thanksgiving 1990, President Nixon went to Vietnam in 1969 and Lyndon Johnson also visited Vietnam twice, and Eisenhower visited the Korean front in December 1952.