I am afraid they are one of the last makes I would consider in terms of reliability and build quality. If you are concerned about ongoing costs I recommend Ford or Skoda. Take no notice of adverse comments about the last suggestion. They will not be coming from people with my background and are years out of date. But drive before you buy, I often wonder why some cars are so popular!
Old mechanic.
Drives ok, a friend with one reckons it eats front discs & pads. I have only ever had 2 Citroens, an Xsara and a C5 and i would never buy another Citroen, had loads of problems with both. In fact on the C5 the Air Con decided to pack up - halfway through a prospective buyers test drive! He did not buy.
Personally the bad reviews I've heard are so bad that I wouldn't buy one. I dare say there are people out there who've got decent reliable ones but in general modern French cars and electricity don't mix and the C4 has a lot of gadgets.
I'd go for a Focus or a Golf or a Mazda 3 instead.