Good:

• The design has been updated and is much less offensive to the eyes.
• The dashboard has better information at first glance.
• Dashboard widgets will probably be pretty cool.
• The new flash uploader is a big improvement.
• The new gallery feature seems pretty cute, although it isn’t the sort of thing I usually go in for.
• Full screen post writing is nice if you have a lot to write.
• Tag management / tag filling is handy.
• The ability to define permalinks on the fly when writing a post is neat.

Bad:

• The admin has a max-width that is very noticeable (annoying) on a widescreen monitor, especially because it is not centered.
• I miss the categories being on the sidebar on the post pages.
• Tags still are not searchable. Why are tags not searchable?
• There is even more Javascript in the admin than before, for an impressive total of 324Kb, ~2 second load.

TBD:

• Whether or not any of the cute little enhancements break the hell out of plugins that I don’t feel like updating.
• Whether or not nightmarish new vulnerabilities have been introduced. With an update this big, it is almost a sure thing.

Watch Matt’s screencast for a quick overview, I have to update the rest of my sites.