As promised in anime topic, here I tell about couple isekai manga where protagonist is NOT almighty overpowered badass.
Isekai ni Kita Mitai dakedo Ikanisureba Yoi no Darou
Japanese engineer ends up going to fantasy world because somebody's mistake, meets a girl, and tries to give a peaceful no-harm impression of himself. Girl thinks he was proposing of marriage and accepts it. Later guy joins adventurers guild to make for a living and goes adventuring. Heavy on slice-of-life, light on combat, and every encounter is a struggle. Characters are likable without being obvious stereotypes. So far so good.
NEET dakedo Hello Work ni Ittara Isekai ni Tsuretekareta
NEET decides to show off his parents he at least is looking for work. What seems like a job offer to beta test new video game turns out a transfer to fantasy world to test out some RPG-like mechanics in live. Except guy has only 1 life without save/load. Looks like an average isekai romp with harem of stereotype characters (priestess, tsundere, slave beastgirl etc.). But in latest chapters protagonist undergoes serious PTSD meltdown, which is done well enough. 1 point for that.