Overall, I can't say this series wasn't bad.
At the same time, however, Seiren seemed kind of dull as another typical slice-of-life romance story.
Can't complain about the animation as it met my expectations, neither diminishing nor raising the bar for this anime.
In addition, the music was subtle enough to provide a good atmosphere for each characters' relationships to blossom. From the girls that Shoichi Kamita (MC) hooks up with or the supporting cast when it comes to tackling the challenges and learning life lessons as the school year progresses, the storyline seems unique in terms of the fact that each relationship is interwoven within the same timeline. In other words, as Kamita moves on from one relationship to another, the series doesn't treat each relationship as independent arcs. Rather, that goes for the end results compared to the majority of time he spends with each girl initially.
In conclusion, "Seiren" seems to grace the theme of slice-of-life much more profoundly than the romantic aspect, though it never strayed from that idea at all throughout the series. And, although, going the normal route may seem the safest route for a romantic anime like this, I've seen my fair share of anime that also take risks and create more compelling circumstances/twists to elevate the anime beyond it's genre.
Then again, while I've seen better examples of romantic, slice-of-life anime, I can't complain that Seiren's more "grounded" approach could really connect more to the audience that that of "Re-Life" for example. Thus, I can't really express my feeling of recommending this series to you, the viewer, as it doesn't resonate with me strongly. But, all in all, Seiren is a pleasant watch so if you happen to stumble upon this, help yourself to something that won't make you feel like you'll waste your time.