Micheal Palmer posted an old B-Greek post of his explaining Aktionsart that helpfully explains the issues involved. In my view, it rather helpfully makes it clear that how Robertson and the other old grammarians used the term differs signficantly from how it has been used in the past few decades. Specifically that the distinction between Aktionsart as the Objective view of an action/event and Aspect as Subjective view of an action/event doesn’t do justice to either how the term is used today in virtually all linguistic studies today or even in the old grammars from the turn of the 20th century.
I had planned on presenting a paper on this very topic at Regional SBL or Regional ETS, but it didn’t work out for me in terms of time commitment.
In any case, his post is worth reading: Aktionsart and Aspect.