I think that actions are more important than visuals when it comes to sexism, so I would say that Agent Aika is a bit less sexist overall than all those shows where the girls are all passive and stuff, or where the only violence is the usual "girls hitting boy" stuff that people have criticized here...
On the note of anime violence, I've said before (as some others did as well) that the amount of hitting in anime isn't right. Teachers hit their students, peple hit eachother all the time... that's not right. In the case of girls hitting guys in harem shows, I think the idea there isn't really that the girsl are stronger than the boys; occasionally that is true, but often it's that the guys just won't fight back against a girl, because no matter how "strong" they are, they're girls so of course in reality they couldn't compete against a guy, so seeing them be violent in the story is considered fine. That is, the reasoning is mostly based on sexism. Yes, men are stronger than women on average, but the contempt of that attitude I just described is horrible.
So, returning to Aika, yes, the series has more pantyshots than just about anything, but Aika is a strong female lead, well able to defend herself and stronger than anyone else in the series. I'd say that makes the series less sexist overall than plenty of animes despite the obvious, constant visual objectification.