The single missing 'feature' (design decision) that I can't live without, is that you can't efficiently do range queries/order-by on the key in riak today.
Hopefully this will get easier with secondary indexes / riak-search integration. Not clear yet.
They are coming, though. That's what I hear, at least.
If we are talking about performing a range operation on the primary key which returns the matching objects, then no, Riak doesn't currently offer that. However, given it's support for an ordered data store such as leveldb in 1.0 it should only be a matter of time before that is possible.
Just to try it out I already implemented this for fun on my fork.
https://github.com/rzezeski/riak_kv/tree/native-range
https://github.com/rzezeski/riak-erlang-client/tree/native-r...