There are the usual checks: make sure that everything electrical works properly, e.g. radio, seats, climate, central locking & remote etc… Then listen to any engine or chassis noises, and look for leaks around the engine bay. Also check occasionally the oil level /coolant level / brake fluid level to ensure they don’t go down for no apparent reason. Check for uneven tyre wear and if exist ask for suspension geometry to be adjusted etc.
Also, if you have access to a code reader then check for any stored fault codes. Check that all the lights in the dash work when you switch the ignition off – some unscrupulous dealers remove the ABC/TC or EML light etc to mask faults.
However – in my view the single most important thing is the cambelt and tensioner (assuming your 2.2 is petrol and not diesel) . These need to be replaced every 40k miles or 4 years without fail (the service book will say 80k/8y, but this has since been corrected by Vauxhall and any dealer should know this!). It is imperative that these have been replaced – and that you obtain documented proof. Tensioner failure spells engine death!