What features do you disagree about?

Cassandra is not a distributed relational column-oriented database, so yes, it will be bad at OLAP queries.

Cassandra is a "wide-column" or "column-family" database, which is unfortunately confusing industry jargon but better referred to as an advanced/nested key-value store. It comes from the original Dynamo whitepaper, along with similar systems like HBase, BigTable, DynamoDB, Azure Table Storage, etc. They can sometimes handle time-series queries with good data modeling because of fast prefix scans but the lack of a real query language makes them a bad choice for analytics scenarios.