Since this is my first comment on this site, I'll try to keep this as brief as I can... Here goes nothing.
When I first started reading this series a couple years ago, I was hooked. I guess I still am, since I'm writing this. However, as time passed, and I reread the available chapters time and time again, I became more aware of its problems.
For starters, the interesting plot now plays second fiddle to lighthearted filler. In the beginning, the chapters were either comedic with underlying drama, or dramatic with bits of comedy to lighten the mood. This near seamless balance is the reason why I invested so many hours into it. The "lighthearted filler" chapters as I call them are actually pretty funny, but there are only so many times I can see Tomoki the chibified closet rapist get beaten into a bloody mess before I become annoyed.
The characters are also kind of hit and miss for me. One one hand, they're pretty original and entertaining. On the other hand, they don't undergo any real changes, save for the Angeloids. Revelations are made about their pasts, but they haven't really changed from how they are at the start of the story. It's fine when their clashing personalities are played for laughs, and in that regard they pass with flying colors, but isn't character development essential to comedies as well?
As for the art, there really isn't much I can say. Everything is pleasant to look at, and it keeps improving from when it started. Tomoki being in his chibi form far too often is the only hangup I've really paid any heed.
This series is still ongoing, so the above problems may be remedied in the future; only time will tell. Don't get me wrong, I don't hate Sora no Otoshimono by any means; I just think it has quite a few problems. Or maybe I'm just reading into it too much. Either way, Sora no Otoshimono isn't great, but it can still make you smile.