The GM Quad 4 family has never been known for its stellar reliability. The original (I'm going to assume) motor went at 94,000 miles. The replacement from a 2001 Grand Am, which had 58,000 miles, went last January.
Wheel bearings needed replacing a few months after I bought it, but J-bodies are known for them going.
I also had a fuel pump go out, which is really just wear and tear, but the dealer replaced it, which meant a jaw-dropping cost of $500.
Besides the reliability issues listed above, I absolutely loved this car.
The exterior looks quite nice, especially since mine was black.
The engine's performance had to have been the best of the best when it was new. Cars like the Cobalt SS, Impreza WRC, and the like have definitely put an end to that, but you can get a Z24 for far cheaper. It also handles a lot better versus lesser Cavaliers.
Fuel economy was not a strong point, however. It only got on average 24 MPG, which really isn't that great for a small car. In comparison, my old V6 powered Cavalier got 30 MPG on average.
While I'm not necessarily in love with the look of the interior (the Cobalt's is nicer), it was definitely packed full of features. Power everything and keyless entry was a plus. The stereo for a stock setup was also really good. It included a six-speaker setup, which included two subwoofers. The stereo itself had nice features like RDS, auto volume, and depending on which key fob that you used, there were personalized presets.
The only feature the car didn't have was a sunroof. I have not found another Z24 besides mine without one.
While I recommend the car for its power, handling, feature content and relatively low price (mine was $5600), I don't recommend it because of the motor's reliability. If you're willing to take the risk, you will buy a what really boils down to a mini sports car. Just look out for non-Z24's with Z24 badging. There are a lot of those "impersonators" so check the engine bay.
For those of you who don't really care about performance, but reliability and economy come first, look at a base or LS Cavalier... up to 2002 they have the somewhat slow but economical and bullet proof 2.2 liter OHV engine. Starting with 2002 LS Sports and standard on all 2003-2005 Cavaliers is the 2.2 liter DOHC Ecotec, which is also used in the Cobalt. It is good middle ground between the 2.2 OHV and the 2.4 engine. It is also known to be reliable.