Seriously. This car needs attention. Do not buy it if you are not willing to give it attention. I'm not sure if I can make that any clearer.
I purchased this car as a graduation present to myself with money that I had saved up working throughout high school when I graduated in 2011. My dad and I are both car nerds. I wanted something that was sporty and had a manual transmission and wasn't your typical Mustang etc. I settled on this car after finding a 2001 Sedan with the manual with ~63k on it.
I will admit that the first ~20k miles were somewhat rough. We probably spent an additional $2-3k catching up on some maintenance that the previous owner had neglected to do, and the dreaded Check Engine light did come on more than I would have liked. Honestly, the vast majority of those repairs were things like oxygen sensors where we could've just fixed it ourselves and have been done with it. This car really isn't terribly hard to work on. I am no mechanic, but I've fixed quite a few things on this car, and it's saved me a ton of money. If you don't feel comfortable fixing it yourself find a good independent shop in your area. The dealer will screw you out the butt when it comes to repair costs. I will say that the car has never left me stranded, and that's not something you can say about a 2001 Mercedes. Trust me.
Like I said earlier. The car needs attention. Make sure to change its fluids and keep a watch out for weird noises, smells, and drivetrain peculiarities (read driveability issues). Doing this will eliminate over half of the possible repair scenarios people have described in these reviews. I'm quite positive that the majority of those leaving negative reviews bought an older BMW expecting it to be just as great on maintenance as a Honda. It is not a Honda; however, if you take care of this car, it will take care of you. Over the last 40k miles or so the only money I have put into this car is consumables (oil, tires, spark plugs, etc), an ignition coil ($75), power steering hoses (~$250), and a dirty injector. I would also like to point out that I would get the manual if I were looking to purchase another one of these, as there are a lot of complaints related to the automatic. The stick is way more fun, it makes the car quicker to 60 (by a full second!), and it's pretty bulletproof. Nuff said.
Now to the part about this girlfriend being beautiful, and I'm not just talking about this car's good looks. This car is THE BEST car when it comes to driving. Not even a modern BMW rivals the steering feel and handling these old E46's have. With the manual transmission this car is sublime. The 330i is comfortable, it's powerful, it handles, and it's relatively quiet. It's not a drag car, but it is amazingly well balanced and fun to drive. Relatively good gas mileage too.
In short, this car is so much fun. Sure, the interior plastics do have a tendency to be brittle after 15 years of sitting in the sun. Sure, parts are more expensive than parts for a Civic. And sure, there are cheaper cars to buy. What there aren't are better driving cars. I've had mine for four years and 60k miles, and the only car I would dream of getting rid of it for is an M3.
Having put 6-figures on both Hondas and Acuras, I was a "reluctant adopter" of the blue propeller. After my first 160,000 miles I cannot say enough about the fabled BMW experience. Not a rattle, timeless looks (IMHO) and the standard suspension splits the difference between firm and comfy brilliantly. The 6- banger is the smoothest ever and the "mere" 175 hp feels like a lot more. Durable? I hit a cow at 60 mph and drove my car home UNINJURED without ANY leaky fluids ($8000 damage). I swear by the 3 platform...
I just passed 245,000 miles and am still using the original clutch, AC compressor, starter, window motors, engine computers and most other parts. With proper maintenance it has been a great car. I average about $300 per month in maintenance but keep it in perfect condition which is far cheaper than buying another new car. At 150,000 the entire suspension was replaced, new brakes and tires. It was like a new car. Still uses no oil, changed every 10K.