While it's good to have some more or less open video codec, the only thing I can think of right now is "missed chance". Even though it's not bad, it's not good either. I would have expected better from Google and On2 considering how flawed the code is after so many years.
Oh and the name... WebM... wtf were they smoking?
edit:
If someone is porting this to devices such as the Pandora, brace yourself for some optimising rework:
Before I go into specific components, a general note on code quality. The code quality is much better than VP3, though there’s still tons of typos in the comments. They also appear to be using comments as a form of version control system, which is a bit bizarre. The assembly code is much worse, with staggering levels of copy-paste coding, some completely useless instructions that do nothing at all, unaligned loads/stores to what-should-be aligned data structures, and a few functions that are simply written in unfathomably roundabout (and slower) ways. While the C code isn’t half bad, the assembly is clearly written by retarded monkeys.