First let me say that I’m not knocking WordPress.
Here are some failings of the new gallery for WordPress 2.5.
The new function is terrific but it needs some work.
This is what I have found so far.
Style tags are inserted by the gallery shortcode into the post or page itself.This is very much not allowed, pages and posts with gallery shortcode will not validate because of this.
Clicking on archives in the sidebar or where ever you put your archives will show the gallery css as the excerpt of the post with a gallery in it, as well as the captions for each image.
The detailed list html is incorrectly nested in the post or page, post or page fails validation.
Alt text only gets inserted on single images.the gallery shortcode skips this, page/post fails validation.
Viewing source reveals this hidden comment:
See gallery_shortcode() in wp-includes/media.php.
Are we to check this file out so that we can see if we re-code ourselves? Fat chance!
Good news, there is a plugin to fix this.
Check the forums for updates on this issue and the plugin.