It took a little while for Solanin to grow on me. Initially, the story, the characters, and the art felt a little too juvenile for my taste. By the end, I'd still agree there were certainly a few immature elements to the novel, but for the most part, Solanin is surprisingly mature.
Ultimately, this is a great story about what it means to be a young adult, journeying from a future of certainty into the world of reality. These characters face anxieties they couldn't have imagined only a year or two earlier. For the most part, Asano's depiction is painfully realistic. The reader truly gets the sense that these characters have very limited options, and that what options they do have are narrowing drastically by the day.
Like most Japanese narratives I've encountered (mostly speaking of anime here), the story jumps around in time without explanation. I appreciate that the creators of these works trust their audience to figure things out. That said, Solanin's occasional jumps in time may be confusing for some readers.
Lastly, I thought the ending was bit too dry, but it was fitting for a novel about average twenty-somethings living out their average lives. Solanin does not end on that note that leaves you wanting more, but it leaves you with an understanding that is not easy to ignore.