I can see why people like this but...

In summary: the first 7ish episodes were completely unnecessary and the show would've been better off without them.
Less is more, right? This show doesn't understand that. The main character is a 34 year old that reincarnates as a baby in a fantasy world and we spend the beginning watching him grow up. Except he's already a grown man (you could make the argument that due to his past as a recluse, he hasn't mentally experienced enough to be considered grown. You could, but that's giving this show more credit than it's worth), so the growing up sequence that drags painfully has little impact. It's supposed to showcase Rudeus' abilities, values, and relationships with other characters as well as personal character traits, but these points aren't strong enough to stand on their own, and the plot isn't interesting enough for this to work effectively. The show makes an effort to give Rudeus character flaws, but in contrast to other character's arcs (especially Paul and Eris, but those are examined later) his "flaws" fall very flat and only serve to make him seem less dimensional. The flaws in question (that are handled in this part specifically) are that he has absolutely no respect for women and constantly sexually harasses them physically or in his imagination, and that he has fears and anxieties due to past trauma. The former isn't a flaw that facilitates growth, and only makes him extremely unlikable and awful to follow as a protagonist, and the latter gets resolved rather quickly and doesn't affect him much considering how big of a part it played in his previous life. Maybe that's the point, that his growth happens within a single episode, but it comes off as lazy to me.
I guess you can also say that his flippant nature is also a major flaw of his, but nothing in the story happens that justifies this until after episode 8 of an 11 episode season. Before then, the only thing we get is that he's a creep that's good at magic, I guess.
And god is he unlikable. If you don't like the idea of a 44 year old in a 10 year old's body making advances on his 12 year old cousin, skip episode 8. I cannot express how uncomfortable it made me feel and how unnecessary to the plot it was. Especially when you have his middle-aged sounding inner monologue yapping about the things he wants to do to women AND girls. Literal chills, and not good ones. If you're uncomfortable with really pervy characters, I'd skip this show altogether. It's constant, it's grating, it's annoying as hell, and if it's a gag it's low hanging, uninspired, lazy fruit. It has nothing to do with the story.
So why am I saying that episodes 1-8 are not needed? Here's what they cover: his relationship with his family (his father, mother, maid, and eventual two younger siblings), his past with bullying, worldbuilding, and characters that are important in the future. I liked the episode about Sylphie, I thought the dad cheating episode was compelling, Rubeus's past is actually informative and well done (then subsequently thrown away), and Eris is an interesting, flawed character (although I'm probably biased because I've watched part 2). However, my opinion that we saw too much of them stands. 8 episodes we spent with them! That's practically a movie, and yet I didn't feel any particular way about anyone other than those mentioned above. Even then, I didn't feel very strongly about them, and there's little to no plot to justify the amount of time we spend getting to know them.
And that's my last problem. I like that the plot starts eventually, some shows don't even have the courtesy to do that. But it starts randomly towards the end of episode 8, and I don't understand why it's barely built up beforehand or why people in this world are so nonchalant about strange things? Like did no one care about a weird orb in the sky or did no one see it or something? The plot kick starting itself feels unjustified after a whole lot of nothing ever happening.
I think this would've been a better experience if the beginning was cut down and the perv shit was cut out. Especially the scene with Eris. That was just the worst. Another nitpick I have is that sometimes the music was really distracting? Like very chaotic string compositions that didn't quite fit the scene they were employed in, and sometimes overpowered what was happening on screen. I can't give a specific examples, but I do remember noticing it a few times.
Credit where credit is due. The animation is very good and the visuals are stunning. The character designs, details, backgrounds, art and art style are gorgeous. Some of the characters are fun, and when he's done being a degenerate Rudeus is can be fun too. But that's all I can concede.
I started watching this all the way in late 2021 and I got to episode 7 before I put it down with extremely negative feelings. Time passed, and I had been watching a lot of mindless isekai and I wanted something more. And I was just so, so disappointed. I don't know why this has such high reviews with such glaringly obvious disregard for the audience's wellbeing in mind. Maybe it's just ignorant, but for something aiming to take itself seriously I'd say that's a naive idea.