St Basil's Contra Eunomius has only very recently been translated into English. I have not yet read it. I have recently re-read St Basil's On the Holy Spirit though. Two provisional thoughts:
First, we need to remember that Basil was profoundly influenced by the theological writings of Origen and is writing from that tradition, as were so many of his Asia Minor contemporaries. Hence we probably need to read up on Origen if we are to really get a handle on Basil's language and to understand his arguments and the development of his thought. Alas, I have not done this reading.
Second, scholars do see a development in Basil's thought on the Holy Spirit between the Contra Eunomius (c. 360-364) and On the Holy Spirit (c. 375). At the time that he wrote the third book of the Contra Eunomius he was still friends and allies with the pneumatomachian Eustathius of Sebaste. He would not break with him until the early 370s. On the Holy Spirit thus represents a maturing of his theological reflections on the person and work of the Holy Spirit. In this work Basil is clear that the Spirit is not a creature and must be ranked with the Father and the Son. Yet even still, St Gregory the Theologian found Basil's refusal to explicitly confess the Spirit as God, of one essence with the Father, quite frustrating.