It's a bit unfair to compare the Omega with anything other than what was available at the same time as the Omega....
^^^^ This^^^^
Below is a list of cars that the Omega would have competed with in the market place:
Dynamically, the E39 5 series is better, albeit a smidge smaller.
The Audi A6 is basically shit, as is the near identical Superb.
Merc W210 dissovles faster than you can drive it and Merc cost cutting of the time makes GM look extravagant
The W211 is better, partly by virtue of being newer, and partly by being better made.
Jag S type a bit left field, but again prone to interesting build quality.
Lexus GS300. Fundamentally fine, but rather beige.
Toyota Camry. As above and wwd.
Honda Leg End. Ditto.
Renault Safrane. It's French and they sold 10 of them.
Peugeot 607. As above.
Ford Mundeo Ghia X. And you thought GM wood trim was crap... Not much going for it.
Sharamblaxy. Has more seats.
Espace. As above.
Peugeot 806/7, C8/Fiat thing... As above but worse.
Vectra C. Estate is a close contender, especially in Elite form, but wwd.
Volvo 850/S80/V70. wwd and more expensive, but good middle class alternative.
Saab 95. wwd and smaller.
Probably missed a few alternatives though...