This topic seems to come up fairly frequently and the answer is: it depends. A lot of the trouble spots for BMW are in the electronics and the N54 turbo motor so if you avoid those you can stack the deck in your favor.
I have an out of warranty 128i, 2009 model which has the N52 normally aspirated inline six and it has 66,000 miles as of this week. I've put a battery in it (you normally get 6 - 7 years out of a BMW battery) for $300 and had two minor oil leaks fixed (oil filter housing and valve cover gasket) for $900. At $95 an hour, most of that was labor.
I plan on keeping the car for a minimum of three years and will be proactive with maintenance. I have a good independent BMW mechanic shop that I trust and they say that the car is in good shape. Hopefully the major mechanicals will prove to be reliable but if not I am keeping an emergency car fund on tap just in case.
If you find a well cared for 3 series with the N52 that doesn't go overboard with iDrive, 4 wheel drive, adaptive headlights, etc. then I would go for it. They certainly do drive extremely well and the inline six is a fantastic overall motor.
Gorgeous photos. Good call on the morning drive.
Like I said, it depends. My independent shop charges $95 an hour. Oil changes for full synthetic are $60 and my shop recommends 7,500 miles between changes (BMW's recommendation can go as high as 15,000!). It seems like the minor oil leaks are common with the N52 and the N54 and are more of a nuisance than something that will kill your car so that is always something to look out for.
This
thread breaks it down much better than I could even though it is specifically talking about the 1 series most of that stuff applies to the 3 series as well. As with all things, do your research, know your budget and make the best decision you can with the knowledge that you have.
G37's are fun cars, by the way. I traded one for my 128i. The BMW drives better, definitely, but the G37 is a solid choice that will likely not have the maintenance issues of the BMW.