Which Zerg units will activate the immortal's heavy shield?
It just seems to me that the immortal would be useless against Zerg with all their light damaging units.

A good amount of zerg units are affected by the immortal's Hardened Shield. They are particularly effective against roaches, ultralisks, and spine crawlers. Also, Psionic Storm and Nuclear Strike do not appear to be affected by the Hardened Shield as the immortal I just nuked disintegrated gloriously.

Edit: I corrected the name of the immortal's spell, and Chops is correct as to why I chose to say "do not appear", as things are subject to change.