The excellent Lara Croft and the Guardian of Light has online cooperative play for Xbox 360, and as of now, so does the PlayStation 3 version. Developer Crystal Dynamics tweeted that the latest title update is now live, enabling the functionality that really should have been there in the first place.
Co-op does make Guardian of Light significantly more entertaining, but that's not to say playing alone isn't worth doing if there's no alternative. If you were holding out for this patch, get to downloading. And as for the PC version and its lack of online support, Crystal Dynamics is working on it.
News on when that's being remedied is coming soon, according to another tweet.
PS3 Lara Croft gets online co-op update [Eurogamer]
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