This manga excels at a lot of points. Its baseball arcs are excellent, the characters are well written and fun to read about, the comedy is on point, and the theme is built upon with expertise.
Of course, probably the 'thing' that sets this manga apart is its main characters. The author managed to create what I call 'attractive' characters; or in other words, characters that draw you in and make for a fun read even if the circumstances or the plot are not that interesting.
As a final note, I have to mention how the author, and his 'style' (his whole style, not just his art style), evolved throughout the series. This did not mean the series suffered a drastic change, though. Sometimes this happens, and in my opinion it usually is never a good thing. Luckily, this manga offers you something from the very beginning, and doesn't change it 20 or 30 chapters later. It evolved, it introduced new characters (at some point, I got a little bit tired of reading about other characters that were not the main character, but, as someone else mentioned here, no character was wasted), and it never got boring.
Of course it has its flaws, sometimes the plot doesn't allow for too much scrutiny, other times the arcs might seem a tad bit unsatisfying in the end, like the finale. I'm not the author, so my opinion is quite irrelevant, but in the end, I felt
that the author heavily hinted at the establishment of a romantic relationship between the main characters. I have no qualms with the author not doing that, but I do have a problem with open-ended-like endings, and with setting expectations and not delivering on them correctly (you can subvert what the readers expect, but this doesn't apply in this case anyway). But, perhaps, more than anything I got the feeling
that the author encountered some troubles with placing these well written characters in the "unknown" environment that was the finale. Nevertheless, the author kind of respected the rule of not worrying to much about resolving all the pending threads, while actually solving some... so, even in the manga's flaws you also see good aspects about it.
And that, I guess, summarizes what I liked about the manga. Even if you see a flaw in it, what's good about it will always shine through. Besides, it never gets too complicated; although the chapters are somewhat lengthy, they are always really 'easy' to read... because of how fun it is.
I read this in (what was basically) two sittings, with quite some time between them. I'm writing this minutes after reading the final chapter, so the second part of the manga is quite fresh on my mind. That said, I consider the whole manga equally good, aside from the ending, and I never really felt the quality dipped.
PD. I placed the spoiler tag in case you're reading this because you want to know the opinion of someone who has read this manga, but don't want even the tiniest of spoilers. What I said doesn't go into any kind of actual detail, but I can't know what's spoilery enough to warrant a spoiler tag.