I purchased an M3 last year after going to the BMW dealer to test drive a 328is. No, I was not pressured into buying the M3 -- in fact, where I live, BMW dealers have such great demand for the M series cars that they couldn't care less whether you buy one or not. Someone else surely will.
So, one year later and approximately 10K more out of pocket, I still believe that this is the best purchase I have ever made in my life! I have not one iota of buyer's remorse. The car is fast, handles beautifully, and is nothing but a pleasure to drive. The biggest drawback: once you drive an M3, you won't be able to drive anything less. You will want the new M3, or even better, the new M5!! But never will you drive an ordinary car again without comparing it to your M3.
Honestly, though, there are a few minor drawbacks: the fog lights get broken easily, the windshield cracks fairly easily (whether this is because of the angle of the windshield, the height of the car, or what, I don't know), and I recently learned that the 1998 has a recall out for the side airbags (apparently, they can deploy if you drive over a large pothole -- very bad).
Buy it if you can afford it -- otherwise, save up until you can buy it -- you won't be sorry. It's a GREAT car!