So this starts out about as generic as an anime series could be - well-endowed girl falls from the sky from another world, literally running right into the protagonist (with a head-butt to the stomach, I'm surprised he didn't get the wind knocked out of him), then she marvels at everything in the modern world, ends up staying at his house - this is probably enough to make your average fan of "serious" anime roll their eyes and/or projectile vomit, and move on. But if that doesn't turn you off, I think this series actually has some potential.
Yes, Nobunaga is a bishoujo, and yes, she falls out of the sky and lands on the main character (actually head-butting him in the stomach). But there's no panty shot involved, and in the end she doesn't stay with Ota, she decides to head out and find items that will help her return back to her world. She seems a little conflicted about leaving at one point, and I think that sets up the potential for some drama later - will her ambition drive her to return to her world and finish the job of conquest she started? Or as they say in Disney movies, will true love conquer all?
Nobunaga is also a great character - she combines abmition, a little tsundere-ness, and an almost childlike wonder at the things in the modern world we take for granted. That's actually one of the many cool things about having a three-year old in the house - my daughter gets that same expression of wonder at things as simple as playing with wet sand at the beach, or a airplane's contrail arching across the sky, or the sunset - all the things that as an adult you generally think nothing of since you've seen them a million times before.
For me at least, Nobunaga alone is a reason to keep watching - and by virtue of having an ex-girlfriend alone Ota isn't your typical loser male lead either. He may be working at a convenience store, but he does have a job. Although he does kind of have Justin Bieber hair like Kaitou in Ano Natsu. I think there's a lot of potential between Ota's feelings for her and possibly (over time) vice versa, and whether or not she'll go home, but we'll see where the writers go with this one.
If I had a complaint, it'd be even in the first episode, while generally the animation and character designs are good, there are a couple scenes that show they're on a budget - much like "Ef: A Tale of Watching People Talk from a Kilometer Away" there's a sequence at the beach where you watch from a vantage point so far away you can't even see the characters' mouths move. But if the story develops into anything beyond mediocre, this will have surpassed my expectations.