IIRC, Riak only did well with the CRDT data types. That result and the rather well done presentation by Peter Bourgon about CRDT and the time series database they built with it at SoundCloud made me look into more, and it seems a quite compelling concept. And obviously proven robust.
Not true, Riak was completely, 100% correct with siblings enabled, which is Totally Expected behavior for a standard Dynamo-style system.
The criticism is that last-write-wins is the default, and that's a fair criticism--that's not an honest default for a robust eventually consistent system like Riak. My guess is they default to LWW to ease onboarding of new users. Everyone is worried about rivaling MongoDB's out-of-the-box experience so you don't scare people away...
TBH, though, if you're using a distributed, eventually consistent storage system without understanding the consequences, you're probably using the wrong tool.
