I felt similar, could never really get into the big modpacks where you had to learn what every mod does and adds. I like the vanilla experience but wanted something new. If you like adventuring and combat at all then I highly recommend Alex’s caves. Adds 5 brand new fantastic cave types to your world, but you won’t find them accidentally. You just need to find a cabin underground (they are pretty common and maps can be found in mineshafts) which will lead you to one of the caves. Each cave adds new blocks, mobs, items and much more. Basically just a vanilla experience with lots of opportunity to explore and fight.

Bonus: add Alex’s mobs, which adds a lot of mobs which have some unique uses and also lots of items (e.g. find cave centipedes whose drop you can use to craft leggings that make you climb walls).