My first BMW was a '91 318is that ran like a top for many years with little to no issues. It was just a great car. I didn't get another one till I was out of college and married. My wife opted for an '01 330i. That car was again very nice with plenty of power and no issues in the two years we owned it. I traded the 330 for an '03 M3 and drive it for a year. I then saw the light and got a porsche.
My wife now has a 530i which shares it's engine with the 330i. It's a little bigger than the 3 series but is basically the same. We have had it for a little over a year and have had no issues at all with it.
Now with all that said I bought an '01 4.4 X5 and had a ton of issues. It was in the shop all the time. Every window regulator in the car failed at least once and when they failed the window fell down in the door and you were screwed if it was raining. The worst problem I had with it was when the clutch on the engine fan seized while it was in the shop and the tech was driving it. The fan basicall exploded and cut every hose and wire in sight. It was out of manufactures warranty so BMW wouldn't cover it, my extended warranty company wouldn't cover it so I was out 5k for all the damage their POS fan caused.
moral of the story - 3 and 5 series = good cars, other models =
$$$