I too find the C4 very attractive, and struggle not to go in and order a HDi 138 Coupe every time I go past the local dealer (just at the end of my road!)
However, my MiL has a C4 - a 1.6 5dr, and I drove it quite a bit last weekend. I am 6' and didn't find the low door line a problem - although I do remember thinking about when I went to the launch at the showroom, I didn't even notice it last weekend.
Generally the car is very nice to drive - pretty responsive and positive (although I wasn't trying that hard as I was only on my TP insurance, and it was foggy most of the time!). The driving position seemed very upright, with high seats, but I didn't fiddle with that except to push the seat back. I found the seats very comfortable - not too much lumbar 'support' which is a bugbear for me in most modern cars. In common with most modern cars, the windscreen / bonnet make a continuous line, which makes for a HUGE dash, and the windscreen being miles in front of you, and the A piller quite obtrusive - ou find yourself looking around them as you drive - although it's only really an issue at sharp junctions / roundabouts. I think this is going to be a feacture of all new cars though, to meet the NCAP pedestrian standards.
The fixed hub steering wheel is a bit odd at first, but you soon stop noticing it. I am not a particular fan of the digital speedo, nor the digital tacho - it's much harder to interpret than a big needle! The brakes are very fierce, and without feeling, so slowing gently takes a bit of getting used to - a bit like a BX with well sorted brakes I guess. The outside door handles are a bit of a triumph of design over function, and the return springs are not really strong enough, and the handles stick in the 'open' position, preventing the door closing. I suspect this will receive attention on later models, as it is very annoying! I liked the speed limiter - I think that would be a very useful feature when driving in unknown areas. Despite only being a 110 BHP 1.6, this car sat on 205/55/16 tyres, so the ride was a bit harsh, and there was quite a bit of tyre roar. Makes you realise just how good the hydraulic suspension is, even when it's not working to 100% as mine isn't!
I was disappointed with the engine though. I expected it to have a good turn of speed, but it lacked any real go, unless you screamed the nuts off it (and even then it wasn't a ball of fire) - to be fair it's done less than 3,000 miles, but I much prefer the lazy low rev torque of diesel engines. The Xantia 1.9TD felt faster when we got back home, and that feels way slow compared to the ZX TD. I'd love to have a go with the HDi 138 though...!!!
On reflection though, if the only real criticsm that you can level against it, is that the outside door handles don't work all that well, things can't be that bad!
Can't wait until they are 3 years old, out of warranty, and cheap! Electrics might be 'fun' by then though I suppose....!!
:twisted: 
(insert a lot of cursing and swearing here)
) Citroëns is allowed to continue the Picasso while Peugeot keeps the stations in the segment with the 307SW.