Only looked at it briefly, but it's one of the (few) things from Google I'm not so keen on. Lack of generics, exceptions, assertions and so on - I know there's been an emphasis as of late of decluttering languages rather than adding loads of features, and to an extent this is a good idea (operating overloading for example was removed in Java and I think for the most part at least this was a very wise move.) However, looks like in GO they've GOne (sorry, just had to) too far. I love the use of generics in complicated code because it often helps to declutter things. Same with exceptions, and assertions are good for checking you've done what you think you have.
Concurrency CSP stuff looks cool though.