Well, rest assured that you haven't made a bad choice and the Omega can be made to handle very well indeed. There are a few common issues that can contribute to it driving badly and they are well-discussed on here. Worth sorting on any "new to the OOF fold" car:
Check the front wishbone bushes
Check the steering idler arm and track rod ends for play
Check the rear subframe bushes for signs of play and generally falling apart.
Have the geometry properly setup by someone who knows the car. In particular, they tend to develop excessive negative camber on the front wheels which causes inner edge tyre wear.
Tyre choice and condition can have a big impact as well.
Many Omegas are getting to high mileages now so condition of shocks and springs should be assessed. In particular, springs breaking is not an uncommon problem.
Careful steering damper adjustment can help if the above still results in a car that wanders a bit.
Even once properly set up, the Omega still feels a relatively "soft" car. It simply doesn't have the rock-hard ride that you might be used to coming from a 4wd car. Chuck it into a corner and it should stick like the proverbial, though, with body roll reasonably well controlled.

Kevin