Been very happy. Did all my own work, and yes, had to replace things, but to be expected with 210,000 kms. I find the car takes care of you if you take care of it. Brakes, battery, intake manifold gasket, alternator, engine mounts (front and back), as well as transmission pulse generator, front exhaust pipe, radiator were needed repairs. Regular maintenance (i.e., timing belt, even oil pan gasket, and trans gasket/filter) relatively easy for mechanical types. Apart from a bit of a combustion chamber carbon-buildup issue (think it is a flaky EGR valve), it is running beautifully, hitting 35 MPG on a recent trip.
Build quality good. Adding a line-in to the OEM stereo was easy (can be found on the internet). Quite peppy - reliable, even at -25C, or +35C. Lots of aftermarket improvements (i.e., struts, exhaust, etc). good power to weight ratio.
Transmission (j39a, aka FN4a-el) sometimes shifts roughly - thanks to the CPU trying to interpret the inputs (i.e., upshift downhill usually rough), but later trans designs in the Mazda 3 supposedly improved. Engine oil seals start to give out a bit early (around 200,000kms). Carbon buildup is chronic.