When the Neuroi occupy Venezia, the whole gang of the first series gets back together to fight them, and the 501 joint strike wing is re-formed. And so we're back exactly where we started off, 26 episodes back at the beginning of the first series. And so all the characters fall into their own roles within the group, and not much happens. (Well, there is some character development, but what character development there was in the first series has completely dissapeared with this 'reset', so it doesn't count.)
For a while, it's about either the wild adventures the younger girls have (going treasure hunting in the caves by the sea, or going on a shopping expedition) and the occasional Neuroi-attack that they have to stop. If you have seen the first series, there will be absolutely no surprises. Even the season finale is very similar to the finale of the first series.
So, it's more of the same. If you watched and enjoyed the first series, then you will certainly enjoy this one. I had the impression that the number of panty-shots was slightly higher in this series, but it might be my memory playing tricks on me.
All in all, I enjoyed it for what it was: a rehash of the previous series. I'll give it a 7: it's not good, but it's enjoyable.
Also, the epilogue at the end of the series seems to hint at another series with a different cast. I'm not so sure I'd watch even more of the same...