Hey mate, my girlfriend owns a 2008 Omega and im not the biggest fan.
For the most part, its a good run of the mill family car, and for what it is has a descent amount of grunt and power, descent sound system, relatively large interior, but if i had my choice (which i did when she asked if i wanted it) i would turn it down.
My personal reasons, are that like most people on these forums, i like to modify my cars, and with the Omega i found it very limited to modifications and upgrades, and the ones that i did find seem to not be as effective as they would be on earlier Commodores.
Simple things like air filters, Cool air intakes, extractors, exhausts ect. Plus the feeling of driving it bores the hell out of me, like im borrowing my mothers car, theres no "bad-ass commodore" feel or excitement as there is again in earlier versions of commodores.
At the end of the day as everything it comes down to personal preference, so don't let anyone tell you that its a 'bad' car and not to get it, as they are a great car, but for what i want out of a car, and from what i've heard most people on this forum want out of their cars, it just doesn't measure up. If i had a spare 12 grand, id be looking more towards the VX, VY, VZ commodore's.
I hope this helps mate and that whatever you decide to buy suits you perfectly.