First, OAuth1's poorly-spec'd signatures make implementation difficult. That's an accepted and pretty well-documented fact.
OAuth2 removes all crypto and instead relies on bearer tokens and SSL/TLS, while not mandating it. It does away with signatures in favour of ease of implementation. [edit] This is a bad thing.
OAuth2 is also susceptible to man-in-the-middle attacks where a malicious party could gain access if it intercepts a token.
That's a pretty poor implementation.
As an identity provider OAuth 1 and 2 have problems beyond the technical interpretation of the specs, or implementation difficulties. Both fail as an identity system (ref. http://www.identityblog.com/stories/2004/12/09/thelaws.html).
I'd love to hear why you think OAuth is a solid solution.