1)Impala isn't a GA offering yet.So as a beta offering, it has several limitations in terms of functionality and capability; for example, several of the data sources and file formats aren't yet supported.

2)Also ODBC is currently the only client driver that's available, so if we have JDBC applications we are not able to use them directly yet.

3)Another Impala drawback is that it's only available for use with Cloudera's distribution of Hadoop; that is CDH 4.1.