Full Idea
Plantinga's critics worry that the metaphysics is actualist in name only, since it is achieved only by populating the actual world with entities whose nature is explained in terms of merely possible things that would exemplify them if anything did.
Gist of Idea
Plantinga's actualism is nominal, because he fills actuality with possibilia
Source
comment on Alvin Plantinga (Actualism and Possible Worlds [1976]) by Robert C. Stalnaker - Mere Possibilities 4.4
Book Reference
Stalnaker,Robert C.: 'Mere Possibilities' [Princeton 2012], p.123
A Reaction
Plantinga seems a long way from the usual motivation for actualism, which is probably sceptical empiricism, and building a system on what is smack in front of you. Possibilities have to be true, though. That's why you need dispositions in actuality.