Perhaps because my first exposure to D&D was the original Baldur’s Gate game, which is full of mock heroism, jokes, silliness and fourth-wall-breaking references, alongside a serious main story of godly ambition and treachery, yes for me this is what D&D is, or at least can be. And I agree that some bits of it are inherently silly, including Elder Brains (which are D&D creatures). Treating them with a level of mock seriousness is perhaps the only tone that would really work for me. As you can see from the responses above D&D can be different at different times and for different people, and I’m sure I have a different perspective as someone who only encounters it through video games and the odd comic from those who are more immersed and play TT as well. But for this particular casual, I think D&D is at its best, and most distinctive and interesting, when it does mix up tones and goes big, and so I’m glad Larian have played up those elements. Though illithids and Elder Brains do stretch it, even for me!
Though I’ll admit that personally I liked the idea of quasi-deities (I don’t think they are literal gods at this stage in the lore) working through their Chosen to regain influence and power. As I understand it, gods in the Forgotten Realms at this time in the lore are discouraged from intervening more directly.
About DnD groups: Yeah, they kinda are a mixture of jokes, heroism, siliness and kindness often. Our group can heroically save a village from undead and then our Firbolg barbarian complains, that her fur got wet and is curly again and my little gnome artifcer goes looking for a tavern to get a sparkly drink with a paper umbrella in it, while our edgy rogue tries and fails miserably in sitting in the corner and brood. All part of the package.
In a lot of instances, I thought, that the game really nailed the tone of your average DnD party. And I also agree, that the first two games had a similar tone, switching between dead serious and utterly silly.
I would like a bit more polish in the last act and making the mindflayer lore a bit clearer. The end is a bit all over the place, with too much handwaving.