I picked this title up a few days after pew pew's releases were showing up in my RSS reader on a daily basis. I'd seen the anime OVA (thoroughly disappointing, though it doesn't fail to deliver when it comes to ecchi) but was still willing to give this a try (the OVA does leave you with the feeling that it could have made a good full series - it develops characters and setting to the point where it's beginning to get interesting, and the stops very abruptly).
The first few volumes are a bit slow, but if you enjoy fanservice and fun characters, you won't find yourself bored as you read through them. Progressing through the chapters, I found the story moving from funny/fun, to good, to great, to significant. I ended up tearing through the last few volumes in one sitting (couldn't stop!), and then found myself eagerly awaiting pew pew's daily chapter releases, all the way to the end.
What begins as a stereotypical ecchi/harem manga transforms into an amazing, complex story that explores human nature, the tragedies of war, love, friendship, the definition of "family", religion, and even touches on the question of the existence of God -- and it's all done with well-developed characters (remember those "slow" early volumes) and without feeling out of place or forced. And as if the plot turning serious wasn't enough, the latter volumes are also filled with great fighting/action sequences that really tie everything together with suspense and a sense of urgency that made me unable to stop reading until there were no more chapters available.
This title does contain plenty of (tasteful though unecessary) nudity and sexual dialog throughout, especially in the first few volumes. Though for the latter volumes, the sexual dialog is gone, and the nudity (still there in full force) honestly didn't feel "out of place" or at all like fanservice anymore.
This is an excellent title that I'd recommend to anyone looking for an epic and thoughtful story, that's willing to slog through the first few slow-paced, ecchi/harem volumes.
Also, be prepared: If you're an emotional person, you'll probably find yourself crying at the happy ending - Happy World! is a well-deserved title.