A lot of recent isekai stories have tried to distinguish themselves by having the hero reincarnate as something other than human within their fantasy worlds. Some of them can get particularly wacky with this idea, but when it works the results can be interesting.
THAT TIME I GOT REINCARNATED AS A SLIME (Tenshi Shitara Slime Datta Ken), based on the novel by Fuse, with art by Taiki Kawakami and character designs by Mitz Yah. First published in 2015 and first published in North America in 2017.
PLOT:
Satoru Mikami is another run-of-the-mill salaryman until the day he gets stabbed to death. Instead of crossing over into the afterlife, he is instead reincarnated as a humble slime monster within a cave. After making a deal with a dragon to gain some senses and absorb some new skills, the newly redubbed Rimaru Tempest plops his way into the world, ready to explore the world.