I had mine from 2007 until late 2015: mishap after cleaning the inlet manifold to try to fix a persistent EGR valve fault (had already fitted new EGR valve so was going through the list).
It was a strong car with very few issues, enabling me to put 120,000 miles on it including Brittany, sideways driving in Scottish snow, beach doughnuts and innumerable trips to the tip.
It just ate up the miles, although now I've got a bargain Picasso HDI the fuel economy of the Omega compares unfavourably. I was getting average of about 33-36 mpg in normal driving. I'd just nudge 41 mpg on a long motorway run at constant speed. In the Picasso (which, despite the Omega's HUGE boot is far more practical) I'm getting mid 50s all day long no matter how I drive.
Problems I had were not really engine-related, though I had a crank sensor go, a couple of electrical gremlins and a pulley break apart. The main problem I had was wishbones and tyres needing replacement. I had the geometry set up properly (not just tracking) several times but it would still go through tyres fast, and the wishbones and bushes seemed to wear out quite quickly. For a few years I made the mistake of putting Eagles on at £120 a corner, which was bankrupting. Mid-range tyres seemed to last longer.
You could get the codes read by a friendly garage to see what the EML is on for.