In descending order of romance-focus, here's a few series that had an unexpected impact on me that I'd recommend:
-
Fujiyama-san wa Shinsuki (I'd actually dropped this early in when I first picked it up years ago. I gave it another shot years later and was blown away. The author's got a real knack at writing immature, young people while still keeping them appealing without resorting to big plots.)
-
Koharu no Hibi (I dislike the yandere archetype, but this has been the only series that turned me around to the concept as a whole. I've yet to come across a character (or series) that straddles the line of uncomfortable-cute like Koharu)
-
Undercurrent (Just a good drama all around. I don't often come across many older female protagonists in the stuff I read, and the series is a good slow burn.)
-
Qualia the Purple (First quantum physics wackiness manga I've read. As crazy a ride as its protagonist.)
-
Sengoku Youko (I keep changing my mind whether I prefer Spirit Circle or this. Sengoku Youko definitely has the biggest finale, which really leaves you with a nice "man that was good" feel)
-
Freesia (Another insane protagonist, only this one actually feels like one. The Jiro Matsumoto style really fits the schizophrenic and cynical perspective)
Haven't finished reading it yet, but I'll second MawMaw's Cross Game suggestion. Adachi's got this really unique style that's a mix of old school lightheartedness and introspective realism; I'm súrprised at how much I'm enjoying it.