If the INSERT statement worked, you should not see any response in the shell whatsoever; it should simply provide you with a new command prompt. This is not simply a quirk of the CQL shell, but a fundamental fact about writing data in Cassandra; writing data does not normally result in any information about the operation from the database, other than an error message if the write failed. Most client libraries will return a null value, or the equivalent in the language in question, when you perform a successful write query.
This may come as a surprise if you're used to working with an SQL database, which will typically give you a detailed feedback when you write data, such as returning the primary key of ...
