It all depends on you really. Do you have the space, tools and ability to work on stuff yourself? If yes, then go for it, they are great cars, fun to drive and not hard to fix. If you are the kind of person who takes every little job to a mechanic, then don't get one.
If you do go ahead with one, what series are you looking at? 3, 5, 7?
The E46 is the best of the 3 series, that goes from 98 to 2006. I'd stick with something 2000 or newer, some of the 98 and 99 325 and 328's had rear subframe issues.
If you want a 5 series stick with the E39 from 1995 to 2003 or so. An E39 540i would be an awesome car to have if you can find one.
7 series I wouldn't get anything newer than a 2000. There is a reason the newer 7's are cheap now, the maintenance is a nightmare.
I have a 2002 330ci convertible so an E46. I bought it 5 years ago with 80k on the clock, my wife daily drives it, except for when it snows, and it has 139k on it now. There are some small common issues with the E46, but they are easy to fix and the parts aren't terribly expensive. I have done absolutely all the work to the car in the time we have owned it and haven't run into anything I couldn't fix myself. That is the benefit of the E46, regarded as the last "mechanical" BMW 3 series. The newer stuff gets a lot more complicated for a hobby mechanic to fix. Also the E46 is better looking than the newer stuff... check out
http://www.e46fanatics.com for more info and research. The 330 is fun, the E46 M3 is a really cool car, but the maintenance is a lot worse than a non M car.
My dad has a 1998 740il. Bought it 12 years ago with 60k on it, now has 190k on it. Biggest issue he has had with it is the catalytic converters going out and costing $1,800 to replace so he could pass emissions. Everything else he and I have been able to fix easily with the parts not being too bad.
Are they as reliable as a Toyota or Honda? No. Are they much better to drive, look at, own? Yes. I'd rather have a BMW than a Camry. But if I couldn't fix the car myself I wouldn't own it. As I said, the parts aren't terrible, but paying a mechanic is.
If you want something more reliable and still somewhat fun, look at Lexus. The car my wife drives in the snow and I drive to keep miles off my truck is a 1997 Lexus GS300 I bought 2 years ago with 130k on it. Legendary 2JZ engine, comfortable, auto climate control, nice stereo, leather, etc. It is fun to drive with that fast V6, not as fun as the BMW, but not as bad as a Camry. Parts are stupid cheap, and it is easy to work on. We have put 20k miles on it and I have done oil changes, shocks and a tensioner pulley.
The 2nd gen GS is better looking than my 1 gen and really pretty nice cars. If you really want a blast look for a 1998+ GS400 or GS430. Fast car, still decent looking, nicely appointed and much more reliable than a BMW. I am going to look at a 2002 GS430 on Saturday to replace the 97 GS300. No real reason other than I have always liked the 2nd gen GS, this one is really nice, and I like the idea of 325hp for some "fun" on the ole commute. :)
