This could be a long review...I'd grab a coffee if I were you.

I came to the C5 after my Audi A4 55 plate suffered the well documented oil pump failure and subsequent welded engine at 105k (fully serviced from new). Audi put their fingers in there ears until I (and hundreds of others in the same boat) went away.

The replacement car needed to travel big motorway miles in as much comfort as possible - I need to get in the car at Calais, and stop for the evening near Milan as an example. The Audi performed well (but nowhere near as well as my previous Vectra 2.0 believe it or not).

So after due diligence, it was a straight shootoff between an Insignia and another A4 - until I saw the big Cat sat opposite the Insignia when I went for a test drive.
The Vauxhall was everything I expected, but I chose to take the C5 out for a run also, and it was chalk and cheese. The Citroen was effortless to drive, at least 60-70% quieter in the cabin, with little or no road noise, and it only had 13k on the clock.

At that time, October 2011, there were precious few bad reviews, and a lot of good ones.

From the moment I drove the car away I loved it. It's a very attractive car looked at from any angle, you don't drive it, you waft along in silence trying to get the mpg down below 50mpg (I can't). It accelerates well, especially in fourth gear which was the best 'join the motorway down the sliproad' gear I've ever had on a car.

Okay, the other reviewers are right...for a car this size there should be far more storage space than there is - you should get more than 3 cd's in a door pocket, and it's physically impossible to use the cupholder if you are in motion, as the centre console needs to be in the 'up' position.
And I'm not used to replacing front tyres every 15k (at £125 a corner). No wonder they have a bad rep for steering rack failure lately.
Open the boot in the rain, or after a shower and water cascades into the boot area from the well at the base of the concave rear window. Cascades.
Also, in a car that is verrrrrryyyyyy lllllooooooonnnnnggg indeed, why aren't parking sensors front and rear supplied as standard?

But it drove so well, I could live with the fiddly stuff.

I bought it in October, and then followed 10k of trouble free, silent and comfortable motoring..... until one morning in June when I went to start it up to find the "Stop, do not drive" light on the dash.
The AA arrived and suspected an oil sensor issue, as it was fully topped up on the dipstick, and the engine sounded fine.
It was towed to my local dealer who examined it for two days under warranty, and found no faults, (the 'stop don't drive' light went out when they changed the oil and filter). They said it was a fault on my previous oil filter, and pronounced it fit to drive.

The next morning at 4am, just south of Gretna, the dash lit up with multiple warnings for less than a second. So fast I couldn't actually make out what they advised, and the engine immediately went into what I thought was Limp home mode. I Stopped on hard shoulder.
AA attended in 30 mins and diagnosed a seized engine.
Car transported back to main dealer (it took four days to travel from Gretna to where I live!)...who after mucho backsliding and threats of litigation, and calls by me to Citroen customer care, replaced the engine under warranty.

After 3 weeks I noticed a distinct tail off in power, especially when 'flooring' to take away from a roundabout into traffic, or overtaking, and a lot more engine noise on tickover and acceleration than usual.
Dealer asked me to bear with it whilst it 'bedded in.'

I bore with it but it got worse instead of better.
Back to the Dealer last week to find...

The Dual Mass Flywheel has been diagnosed as shot, and is being replaced under warranty.

Better still, they suspect the turbo is also damaged, but won't know that until they replace the DMF and check out the performance.

Luckily, this is still under Warranty and Citroen have paid for everything, but had this happened next year, I would have been out of pocket....

£7000 for a replacement engine and labour.
£1200 for a replacement DMF
and a potential £1400 for a new turbo.

Just shy of £10,000.

I'm not saying don't buy one, because I think I've just had a 'one off'. But just bear in mind the numbers involved here. Ten thousand pounds to fix it. So far.
Ten thousand. And I haven't yet experienced the steering rack failures or driver side window motor failures that now seem to be manifesting themselves in 3 and 4 year old cars.

It's a big, attractive, comfortable, head turning economical motorway cruiser that is perfect for what I wanted it to do......but it just keeps breaking, and I'm here on Honest John hoping what's happened to me will help guide others in their choices when considering the C5.

If you get a good one, it will be everything you ever wanted in a car, but if it does start to go wrong, IMHO get shut of it asap, which is what will happen to mine when it eventually gets out of the dealership. I'm taking the hit and going back to something Teutonic.

Sorry to bang on....I'll get my coat.