Having watched both IRIS and Athena I felt compelled to write the review for the former mentioned show.
Athena has some good action scenes, however some of them feel a bit forced and overdone. How to put it more clearly and bluntly? Some of them feel too unrealistic and you have a feeling that it is too fictitious and not believable. Same thing was present in IRIS but in much less quantity.
Next minus is the suspense. Instead of a flowing story arc there are subplots which don't fit so well one after another. They are not so compact. The transition itself is good, but after it ends you feel like it had no big impact on the story as a whole (I am referring to episodes 3 to 5).
The last great flaw is the drama, which in the absence of better description from my part is not up to par (not satisfying enough), it lacks more storytelling and exploration. The kind that was done well in its sister show IRIS.
However there are some pleasant surprises in this show and the end does have closure, although the last 10 episodes are somewhat dragged out when it comes to storytelling.
All in all I found Athena as a good, solid show which lacks some pace, suspense and more deeper drama but it makes up for it in a good measure of action, acting and immersion into its world.