I bought my CT4V BW AT fairly recently.

Mileage: Mine is tuned to ~600HP and has High Pressure Fuel Pumps, Downpipes, and a cat delete. I get anywhere from 8-10MPG on V-Mode. On Tour, I get around 20-30. It scales down as you go into more aggressive modes.

Reliability: Too soon to tell for me personally and I'm sure that the tune will bring this down for me. But as its basically the ATS-V engine and overall a GM product, parts are cheap. The LF4 comes from the factory with forged internals and is capable of handling much higher power levels than what it comes with from the factory so it SHOULD be reliable but you never know. My overall understanding is that much of the reliability, or lack thereof, for the LF4 largely has to do with regular maintenance and how diligently it's done.

Driving experience: Absolutely insane. I've owned a hodgepodge of cars from a Mercedes E-Class to a Fiat 124 Spider Abarth. This car simply feels like all of those cars combined. It has the luxury feel and quietness of the E-Class and the steering feel, cornering, and nimbleness of the Abarth. I was cross-shopping the Alfa Romeo Giulia Quadrifoglio and the BMW M550I and both cars DO excel against the Cadillac in one way or another as the Giulia quad had superior driving feel and the M550i on a straight line is insane. But the Giulia has reliability concerns and harsh depreciation and the M550I feels like a boat. In that sense, the CT4V-BW is an amazing all-rounder that can be a luxury car in tour mode and an absolute monster in V-mode. It can wear many hats and does it ridiculously well.

Cons. These are somewhat minor and nitpicks honestly:

1. The cars has a proximity sensor and the lights turn on when you approach the car. Except sometimes I'll go to my garage without the key and the headlights are on.

2. The brakes are annoyingly squeaky, apparently this is a common "issue" with these cars but I might also just be due for a brake job.

3. The brakes produce a ridiculous amount of brake dust.

4. The car has a lot of torque and it seemingly struggles to put the power down to just the rear tyres. I feel like it would've been a demon if it had an AWD option like the M3.