Well, that was quite a good read, wasn't too amazing, but still enjoyable for a shounen.
It felt a little more mature than usual shounens are and the protagonist who isn't actually whiny kid is a breath of fresh air.
I also am not sure why people say this lacks fanservice... fanservice is literally in almost every chapter here - certainly more of it than in any of the 3 big whales(Naruto, Bleach, OP)
Also the fanservice wasn't too out of place like some ecchi comedies do.
Was considering giving it 7/10, but since the mangaka made up a well drawn conclusion I will give it 8/10, since I suppose he was only given around a month to make it - it was really a great job. Revealed some story elements and characters whom we would probably see a lot later in series otherwise to give a general idea of what was supposed to happen in near future and still giving a rather fine open ending it deserves.
Among shounen series - this is easily one of the most promising one I read. But then again - bleach and naruto were really great for the first couple of arcs as well, only losing their charm much later on and started being rather terrible by the end, so it's still too hard to judge normally.
OP is still going strong, starting the weakest amongst the trio, but remaining strong throughout the whole lifespan.