I have a 2017 LR Discovery HSE Td6. The electrical system, which as a platform (D7) is largely shared with the Defender, has been flawless - the only problem there was a failed keyless entry module that the dealer fixed under warranty in 2 hours including time to reprogram the new one. Didn't keep me from starting the car or securing it - I just used the activity key.
Drivetrain wise - the ZF 8-speed (8HP) that LR uses is the same one that multiple automakers the world over use. It's ubiquitous, reliable, very tough. The basic unit is rated to over 600 hp and 600 lb-ft and is used with the Ford-developed AJ V8 engine that's rated over 500hp in the Range Rover Sport SVR and the Jaguar F-Type SVR; it's also found in the Porsche Cayenne, Lamborghini Urus, all manner of RAM trucks, the new Supra, and on and on. For me it's been bombproof including in off-road situations shifted manually with the paddles. The current 3rd generation box has been designed with mild hybrid/KERS systems in mind, as is found in the new Defender.
Can't speak to the MHEV P300 and P400 engines in the new Defender, so always consider the factory extended warranty when something new like a brand new powertrain shows up. I bought one with my 2017 Disco and so far...it hasn't paid for itself, but that's actually good news.
Generally, it seems most people who are technically inclined seem to enjoy the Pivi Pro infotainment as it's quite stable and much quicker than the old In Control Touch Pro that my Disco has, but most complaints with modern vehicles comes from infotainment frustrations. The more the car costs, the less drivers are willing to put up with infotainment glitches, but they affect every single automaker. Even Consumer Reports acknowledges this.
Terrain Response 2 - the Defender has more adjustability in terms of center diff locking behavior than my Disco, but it's largely the same. It's never overheated any of the diffs, it's bailed me out of tricky situations including 3 wheels on ice and one in a hole in the ice over a mud pit (AT tires, not even snows, and not studded), and climbs like a goat over all manner of babyheads and other loose stuff.
Air suspension - seems vastly more reliable than previous models - but there are wear items like the compressor and valves, and while the bags have been strengthened, they're still rubber, but I see no reason why 150K+ miles should be well within the lifetime. I'm at 60K and never had a problem - not even in -20F weather where old systems tend to show their age.
Go poke around the various LR forums out there. LR suffers from the ghosts of the British Leyland and BMW eras - since the latest generation of vehicles began arriving in 2012 they've been much more reliable. Still room for improvement for sure, but the days of having to keep some extra harness smoke in your glovebox are long gone.
I now see more new 110s on the road than I do Discoverys, but I see quite a few of them too.
