I guess I'm a bit set in my ways - I have no intention of using CQL (does that C stand for Cassandra or for Collection or for someting else?) which I'd presumably be stuck with if I were to use Apache's Cassandra API, I prefer things which are not designed to encourage denormalisation. So not supporting that API seems to me to be a CosmosDB plus point. Not that I expect ever to use CosmosDB either, mind.
Of course from a classical point of view, Cassandra was always the bringer of bad tidings, predictions which no-one believed until bitten.