Faults:
Lots, mostly electrical, too many to list. The worst was a crankshaft sensor - car would not start, took my mechanic a bit of time to figure it out and get it going, but was not as much to fix as I thought. Apparently a common fault on Omega's. The rest were minor irritations: electric windows slow, air stopped working, etc.
Mechanically the car was not as bad as people made them out to be. The suspension and brakes were replaced at higher mileage as you would have to do with any car.
Engine and gearbox wise I never had any major issues, I kept the car serviced on time and belt changes. The bodywork looked very rough in its final years however.
General Comments:
I really like these cars, despite their average reputation for reliability, and a half baked attempted at taking on the executive market. The Omega is however underrated in some respects. Having owned most of the "premium" executive cars in the past (BMW / Mercedes) I can confirm the Vauxhall Omega is just about as good to ride in, very quiet and smooth. Handling wise the car is a little sloppy, but everything else was OK.
The most basic model, the GLS, is what I had, and is still well equipped with electric windows, alloy wheels, etc. 2.0 engine has decent performance with over 30 MPG possible on long cruises. I would definitely recommend going for a V6 though - much more suited to this car, and an auto box, as the manual box feels a little vague. That's not to say it is bad to drive - it is not. Just not as good as an executive car should be.
Absolutely love the look of the car in dark metallic red with the 5 spoke alloy wheels, which were on the car when I bought it used, I believe non standard taken off an Elite model, really good looking wheels. And the 94 - 98 Omega is the best looking, I was not so keen on the updated 99 - 03 models. Interior is nice as well. Space is generous and has a big boot.
Back in 2015 I sold it for more close to what I paid for it back in 2005. Ironic, as when new they depreciated like hell. It was always a much better used buy. So I definitely got my monies worth out of this car. Had they been a bit more reliable, I reckon they might have been a better contender to the bigger German brands. But the car itself was just as good as any executive offering from the time period.