My issue with D&D isn't that it's "kiddy" compared to others (the World of Darkness settings were infamous for their juvenile settings and tropes back in the day), it's that the majority of the actual printed content, is predominantly devoted to combat. It's either talking about feats, and gear, and combat rules, and magical spells that are almost all combat oriented. Where if you counted up the pages in each publication that are devoted to the story/setting, versus the combat stuff, it's probably like 75-80% of it for combat. Which I frankly just get bored with. I don't play roleplaying games just to be battle simulators, that's what I have video games for, and I don't really want battle simulators out of my video games either. I prefer games that encourage more narrative, "theatrical" play. And D&D just doesn't do that. You CAN do it sure, but the onus is entirely on the GM and the players to do that, because the published material really doesn't give you a whole lot to work with.DnD isn't completely without merit, as it is a fairly well rounded system for swords and sorcery, but I think there are very few experienced RPG players who don't rewrite at least some of the rules. Frankly, the same can be said for most RPGs. Vampire: The Masquerade 20th Anniversary is the best version of VtM by a considerable distance, but my group has still tweaked a lot of the rules, and shoved in some systems salvage from V5 as well.
And this isn't unique to D&D in my experience, a lot of roleplaying games confuse ROLEplaying with ROLLplaying, and devote too much time to the crunch stuff, in my opinion. It's one reason I've sort of fallen out of the pasttime, as it's just not what *I* am looking for in a table top experience.