Why is it that most reincarnation light novels are blatant wish-fulfillment?
They all start with some quite nice world building and a good concept, but it often devolves into "I can do this, I can and will do that!" and a few 8 year olds becoming too close with the protagonist.
Mushoku Tensei is by far one of the better ones, among the ones I've read. Protagonist might be overpowered due to a head start in knowledge and an iron will, but his hubris tends to result badly for himself and his allies. Said thing devolves a bit though once it reaches the unnecessary s*x parts. [Any reason why the guy has to have three wives?]
Tensei Shitara Slime Datta Ken is like Re:Monster in which the guy gets some powers that allow him to absorb powers from his foes. It personally sits somewhere on meh-tier, and I didn't finish reading near the end of the first arc, since the guy is just power-gain after power-gain, aimlessly.
Re:Monster starts out interesting, peters out in hypocritical actions from our "hero", in which he [lewd]. Otherwise good enough, but is still power-gain after power-gain in a rapid growth-state.
Gunota ga Mahou Sekai ni Tensei Shitara, Gendai Heiki de Guntai Harem o Tsukucchaimashita!? or AKA the overly long title that most people just call Gun-Ota, is a rather interesting thing. Our guy is reincarnated in one of the more bloodiest intros in the reincarnation recreation thingy thing. Then he wakes up, discovers he doesn't have much magical ability, but from his previous life was a metalworker addicted to guns, and upon discovery of a special liquid metal, decides to recreate gun technology.
You'd hope said thing is interesting but unfortunately it loses its steam rather quickly. Guy gets married early game and is introduced to another heroine. Also, was there a point saying that the first heroine had C-cups at age 8? >.> On the second part, he suddenly knows enough technique to cook some snacks and is apparently an apt storyteller. There's a wide gap between one weapon and the next during that time, and I ended up losing interest because the guy was suddenly far more skilled than he should have been.
All in all, there's a quite sizeable library of these things now, but I don't think any one of them has pulled a "grand one" yet. RE:Monster is fine as it is but it's just power levels after power levels, and people fawning over a smart goblin. Mushoku Tensei already concluded, and might be worth a read, but there are some glaring flaws to it if you ask me.
None have yet pulled a reverse-reincarnation situation yet, in which fantasy guy dies and is resurrected on the modern, real world. Hm.