Not so much for the design (oh look it's white instead of black, who cares), but the way they've handled it subsequently.
The 3.x -> 4.x transition for Kibana left a product that was missing really basic features (like, the ability to set graph colors for one - a bug/feature request that's been open since last january).
As it stands, upgrading from Kibana 3 to Kibana 4 is a step backwards. You lose functionality rather than gaining it.
They also decided to require a major version bump to Elasticsearch (to 2.x) with a point release of Kibana.
I used to be super optimistic about the Elastic guys, but some of these decisions are just head-scratchingly awful.