Yes, this does seem quite serious.
First ever Iranian attack on Israel from Iranian soil - IDF
A former Israel Defense Forces spokesman, Jonathan Conricus, says "this is day one of the new Middle East - for the first time Iran is attacking Israel directly from sovereign Iranian soil".
Speaking on the BBC News Channel, he cited reports of more than 100 Iranian drones and cruise missiles heading to Israel, "with different expected times of arrival". He said "Israeli air defences are busy taking out these threats".