The first and most important thing is, please do not forget that this is a manga adapted from a Light Novel. People here tend to give bad ratings only because they do not seem to be able to read the exact same things they did in the LN.
You cannot expect the same! Please ignore those reviews.

Mushoku Tensei was one of my first mangas from the "Isekai" genres and I fell in love with it.
No bullshit harem building, no super overpowered hero, no crazy abilities just a man who dies and gets reincarnated as a baby to loving parents. With knowledge from the old world and his real age, the main character was able to learn and understand things like magic and stuff a lot faster than normal people his age.

The art is really good las most of the animes, the pacing is also fine and the most important characters have a well-written background which is enough for a manga. People expect things like story writing from Eiichiro Oda here.

If you are a big fan of the Isekai genre or if you just became interested recently then this is a must-read, it is probably better than any other Isekai manga.
Please do not get scared from reviews which low points because thats not what the manga represents.
Thanks for reading!