I know what you mean, I felt that way too. I think it's probably that because of how long it took for the seme (musaka?) to remember who he was there wasn't too much romance. Also a lot of the characters were underdeveloped, and they didn't really have a comeupance for the badguy.
Also maybe more smexy scenes ;).
Ugh.... It cut me off....
Generally when it feels like something is missing from the story, it's a pacing issue. Parts of the story are too rushed and parts are glossed over.
I felt that in this instance, it should have shown Kousaka falling in love with Misaki while he still thought he was Yanagida. Also... The "you promised to fuck me on the 5 year anniversary of the death of the love of your life" plot line..... That doesn't really work for me.
They seemed to keep pushing that aspect of the story without showing the MCs getting to know each other as strangers. I would have liked a bit more romantic tension before the act 3 sex scene.
I love the manga and i love all the characters including megane-kun but I felt like if there was something missing and I don't know what but there was something missing time spicy up the story.