These types of threads are often because of un-informed people.

German cars are no more or less reliable than any other car made in any other place (of course there could be exceptions and models that have issues). It is a car, it requires matinence, and when this is done on time and correctly the car will run properly.

The issues people often run into with German cars is that they are better equipped than many similar cars on the market. This causes you to have more "things" in the car that could break or need upkeep.

I have owened many German cars (mostly BMW and Mercedes and a couple VW's), many Jap (Nissan, Datsun, Toyota, Lexus, Mazda) and a few odd balls as well. None of them are more of less reliable, but some of them have matinence needs that others would not.

So if you are willing to pay the upkeep costs for your selected vehicle and to do it on time you will do just fine. If not.....buy a Honda.

So... subframe cracks on sedans common?

Not 100% sure on this answer, but from what I learned subframe cracks are more common on pre-face lift models (1999-2001) coupes more than sedans, Convertibles even more. Less incidences of later models developing cracks. (2002-2005; 2006 for coupes)

M3 regardless of year I believe are not immune to subframe cracks.

If you search "*** Sub frame Damage *** Sign here if you have this Problem (Letter to BMW)" you will see a list of people who have this issue. Take a look at the list, most are earlier model e46

e46 known for their cooling systems failing, at around 150k(give or take a few)

Here you go:

Edge Motorworks - List of Common Problems on E46 @ 75K Miles (M and non-M cars)

I think for most people when they think "reliability" I don't think they mean just the engine itself. It's usually things like electronics that fail. You can't exactly maintain a power window motor or some sort of sensor.

When you have to replace something electronic all the time, it tends to be a design flaw due rather than lack of maintenance.

I've personally only had one mechanical issues with any Euro car, but electronically had tons of issues with my Euros. Maybe it's just shitty luck. But when multiple of my Euro's have these similar issues, you tend to get jaded. Can't exactly maintain an OEM alarm, fuel sensor, TPS, etc etc.

it's a pretty reliable car. Used to own an e46 sedan.
But of course it needs more maintenance done compared to japanese cars.

keep up with your maintenance and you wont have components breaking on you when you need it.
For example, the coolant tank on these cars are notorious for cracking. In some japanese cars, these are parts that you probably will never replace, but for these it is recommended you replace every 100k kms.

Pay to play.