How to know if these congresses (i.e. organized by ISCA) are good?
Consulting the Australian Computer Science Conference Ranking reveals that one of their conferences, CATA, is ranked C. I did not check any others.

Indicators   that the conferences are not good include: 


The conference is extremely broad. CATA covers topics including Algorithms, Programming Languages, and Multimedia. 
The conference is in an exotic location (e.g. Hawaii).
People involved in the conference are not the leaders in their field.
Conference is not well established.
Conference does not appear in the Conference Ranking list, even though it has been around for a long time.


Note that conferences satisfying some or all of these criteria are not necessarily poorly ranked.