Yea I think this was it exactly, and great point with the visualize of Dark/gloomy vs. bright/colorful when hes with the sisters (Momo is adorable btw). I feel an issue I had was I wanted to sympathize with Rei more but I couldn't as I felt even in the info they provided, I still felt there was a lot of info about his upbringing which lead him to be who he was left out or not gone into detail of. I knew his parents death in the car accident affected him greatly, however his adopted father loved him ( I know his sister hated him which I also feel their relationship is extremely odd, it seems she had sexual feelings for him & that he keeps letting her just coming into his life/apartment even though she's a terrible person) & his shogi friends seems to like him too, and since hes been playing that for a while, I assume hes known them for a while.I think it can lag if you just don't sympathize much with Rei/the sisters or the sport of Shogi - this was a slight issue for me and I'm guessing this is part of your issue as well. By the second season Rei has realized his value and there's more focus on developing the issues of the side characters. I think it's realistic to experiences in modern Japan. Maybe not the U.S.
I also wish they used the sisters more than a shining light for Rei + food as there seems to be great development and material that could be gotten out of them (Their lives/depression).Like you said as well, the shogi portion don't really have much interest in and it seemed like 10-15 episodes were geared specifically for the sport itself more than actual story, episodes seem to drag because of it.
I will be checking out s2