Greater selection of "adventure type bikes" is probably the best thing that has happened in the last 20 years....Not much improvement in components or anything else.
Here is a list of things I don't like:
- newer cranksets with direct mount chainrings...I hate those and I am still using the older 4 and 5 bolt designs
- internal cable routing...I just hate it
- thru axles... I am still using nutted axles and quick release axles
- different axle spacing standards...I have two bikes with 135mm spacing and one with 120mm spacing.
- way too many different styles of disc brakes and each one has different pads... It's a jungle out there for brake pads.
- tubeless tires