I put off reading this manga for a while since I saw the plot and thought, "How can a 10 year-old be a harem lead?" It's a fair question, and it should be enough to make people want to put off reading this manga. However, soon after I started reading it, I realized that this isn't a typical harem manga. This isn't like Love Hina. The main focus in this manga is not a character (or characters) falling in love, but rather a boy (who is obviously mature for his age, but not in the love department) who goes through the trials of trying to obtain his goal. Like many other manga, there is a side story of love, but this is barely touched up on. There will be chapters, or maybe multiple chapters, dedicated to developing this aspect, but other aspect of the story (gaining strength to obtain one's goals) takes up many more chapters than the love chapters.
Now as for the criticism I've read so far, I have to say that this is mainly due to people always wanting to read the greatest thing ever when they pick up a new manga. People say the story is simplistic. I have to say, so what? I mean, there are manga out there with philosophical meaning behind the story, or that contain many twists that will make the reader have to step back and say, "Damn. That's crazy." However, not to come off as a jerk, but if every manga was complex like that, there will be fewer manga readers than there are now. People like simplicity. It's straightforward and doesn't require you to take a step back and think about what you just read. I mean, if you want to read philosophical manga, or things of that sort, than you should read them. Don't try to put other people off from reading a manga because it doesn't fit your tastes. It's easy to say, "This manga won't make you think. It's all straightforward. It doesn't suit my tastes, but it might suit yours." That comes off much better than, "This is the worst manga ever. Don't even bother reading it." What may be the worst for one person, may be the best for someone else.
People seem to unfairly criticize fan-service. BTW, fan-service does not only refer to ecchi scenes (although that is a majority of fan-service). I mean, if you really hate fan-service to the point where it makes you hate a manga, than you're going to have a hard time reading any Shounen manga. Yes, there are ecchi scenes in this manga. Is it so overbearing where you can't go a single chapter without one? No. They give you plenty of time to breathe. Believe me, I have read manga that are much worse in terms of the amount of ecchi scenes.
So, lets wrap this up. Overall, I would give it a 10. It's not the greatest thing I've read by a looooong shot. However, it is still an enjoyable read and many people can find this to be entertaining. There are ecchi scenes, but not enough to make it overbearing. It is not very deep, and it will not make you sit back and say, "Hmm, that was quite an interesting chapter. Let me discuss this with the rest of my pseudo-intellect companions." However, it will make most people laugh and the fights will make most people say, "That was pretty cool." I recommend you read it before you let someone's opinion put you off from reading it.