Wow. Usually the reincarnation/time travel/revenge thing is generally pretty terrible and predictable. From what I've read the results range from "dumpster fire" to "toxic-waste-disposal-site-conflagration" on the "trash fire" scale. This isn't even terrible at all. MC is a little OP, but he still faces some reasonable challenges. There are a lot of twists, but none of them feel like facile ass-pulls (which makes it the exact opposite of SAO).
If I had to level a criticism the MC is a little too much like Archer from F/SN, but he doesn't elicit any feelings of GAR. This is a pretty petty complaint. Otherwise this manga is surprisingly competent. It's like it was written by someone who actually knows what a decent story is. The art is very clear and good too.
This is easily one of the best manga I've read in a long time.
For all those who have noticed that: https://mangashow.me/bbs/page.php?hid=manga_detail&manga_name=라그나+크림슨, doesn't work anymore, go here: https://newtoki10.net/comic/109016/b]