Probably the obvious items common in an IDI diesel designed by VAG in the '70s with its corresponding high CR (neighborhood of 23:1) as you note. Combustion chamber is actually similar to Ricardo swirl chamber with a small turbulence/heat-inducing porthole into the cylinder.
Bottom end appears to be stout, as inspection shows they are almost always in great condition even with high miles. The D24(T) version got piston squirters.
It's what's known as a "hi-rev"
diesel.
The Al head, being a long L6, can warp if overheated. OHC.
Main problem was VW's idiosyncratic TB/cam pulley/crank pulley/injection pump timing engineering solution what was non-common and
required special tools and procedures that if not followed resulted in sure catastrophic engine destruction for this extreme interference fit example. Bent valves, damaged pistons, broken camshaft, tappets, etc.
For example, TB R/R requires over 350 lb-ft torque on the crankshaft pulley bolt. Who's shop is set up to achieve that reliably?
On the highway
(aware I am going to get flamed for this bigtime:) it is much more refined feeling and less busy than a 4-cyl redblock.