DotMM in 5E is an updated version of the Old Dungeon that compacts the amount of content of the old dungeon versions from prior editions into a much smaller space. Modern audiences are (for the most part correctly) thought to have less of an attention span and will be less interested in finding a majestic empty ruin ... and instead want their next combat fix.
However, it is still a megadungeon and that is different than an adventure. While you have light threads of storylines, the dungeon is mostly there to be explored. The point is, really, that there is little point to exploring it other than to explore. As the megadungeon can be mostly bypassed, or explored in random orders, it is hard to have sequential storytelling in it that doesn't get hashed up by the party.
Regardless, even for a Megadungeon, I find the 5E version a bit flat. The minimal storylines are not engaging, the combats are pretty vanilla, and the environment, while changing from level to level, does not create evocative combat situations. It was very much less exciting than I expected it would be - and I am enjoying the product less than I enjoyed prior delves into Undermountain decades ago. However, when given the chance between Megadungeon or campaign with a storyline, I much prefer a storyfocused adventure.
I believe there to be better 'Megadungeon' products out there for 5E. Rappan Athuk, for example, has a lot of fans.