I think the series that impressed me the most last year was a late arrival - Unexciting Date. It's easily the best dialogue I've seen all year (since Food Court de Mata Ashita is still stalled) and it's an oddly satisfying slow-burn romance (with their awful communication skills, any romance at all is an impressive accomplishment).
As far as ongoing stuff goes, I'm still very impressed by Boku dake ga Shitterun daze aka Only I Know. It's a somewhat typical young romcom that's most notable for the MMC - Waku - who has a lot of the cliched reflexive reactions to all this nascent romance stuff, but instead of just allowing himself to be subject to them, he stops and considers why he's reacting that way and what he should be doing instead and, most notably, what would be best for the FMC - Oura - then he steels his resolve and does what needs to be done, and it's such a pleasure to watch.
And Renge to Naruto just gets better all the time. It started off as just a sort of goofy ecchi comedy with an enthusiastic gyaru running a Chinese restaurant and a sort of quiet and awkward working stiff who becomes a regular, but over time it's morphed into an impressively subtle and complex character study/slice of life/rom-com.