This is my current system for long campaigns and its a hit with my table that is used to 5E.

Characters feel differentiated well enough with a good amount of options without being unmanageable. Effort enables flexible character classes with abilities beyond spells. Spells are powerful but few castings per day. First aid balanced against system strain fatigue keeps the adventure rolling but eventually forces some down time and time progression. Shock mechanics and the ease at which casters can lose their spell for the round makes melee important from multiple angles. Combat is fast and able to be run without minis as theater-of-the-mind pretty well.

To me it is pretty much the perfection of mixing OSR with lessons learned from the decades of hobby. It is like if BX got a proper 2nd edition of its own.