I'll say one word! UNIQUE CONCEPT OF LOVE.
usually we watch the kind of love where a boy confesses when he realises that he's in love. But this was quite different so it grabbed my attention. The Love of two childhood friends and the love for Baseball, was portrayed well.
Kang Baek Ho's (Yoo Seung Ho) intense feelings were prominent through his eyes, but unreachable to the mouth because of his shy nature. Ham yi seul also had her unique charismatic personality that made us watch the whole series. So the acting was amazing.

The way they were so desperate for each other made the audience love their couple. A very unique concept of love. Plus the idea of how someone can't change anything by regretting over the past is captivating.

Major flaw:

what disappointed me was Constant repetition of Baseball scenes and unending regret of kang baek ho. It was interesting in the start, But in the mid it became a torture. I just had to complete the series. No development in characters. No twist. No thrill. The Drama was being DRAGGED to the end.
For Yoo seung ho 's fans, It's okay. For the High rated kdrama lovers, you can't watch it.