When they say slow life, they really do mean it. As in nothing interesting happens. There is no motivation, no suspense. It's just a plain guy living life with pretty strong magic which he does nearly nothing with. In other "slow life" mangas where there's a demon lord, the protagonist has an actual goal, which is to gain a "slow life", and goes through various conflicts. In here, we are introduced to bland characters every few chapters, and that's the only form of fun there is besides him using magic or using modern knowledge, which gets kinda bland. Another point is the family and him getting picked on. It was maybe funny the first few times but it gets annoyingly repetitive and is mostly unwarranted. If there were more scenes of them getting along, then maybe the harassment is okay as a form of bonding, but nearly all his interactions with the sister is him getting hurt. All we know about their relationship is that she hits him, and maybe they have fun sometimes. Nothing else.
Overall, gets boring fast, and the only parts where my hearts gets pumping is when it get annoying, which is three quarters of the time.