The M54 is the most reliable BMW engine ever built. Here's why:
The camshaft chain drive and the V-belt drive are maintenance-free and designed for the life of the engine.
Valve clearances are kept consistent throughout the entire running life of the engine by a self-adjusting hydraulic valve clearance mechanism. There is no need to adjust valve clearances, ever.
There is no need to reset the clutch since it is self-adjusting.
The air filters and spark plugs only have to be replaced after 100,000 km or 62,000 miles.
The oil in the transmission and final drive is a lifetime filling not requiring any replacement.
The engine is able to adjust automatically to all fuel grades between 87 and 98 octane.
Anti-knock control automatically adjusts the engine's running conditions to the respective fuel grade and quality.
Copied and pasted (what did you expect?)
FWIW: It was the M50 that sold me on BMW, after driving a 1992 5 series with 180,000 miles on it. The M54 just improved on the M50 and M52.