There's a 36-page thread about fuel consumption (top of the forum) - takes hours to read - basically, 8L/100km seems to be what you can expect, a little worse than your BMW I'd imagine
needs to be compared against, say, a hypothetical 2.4L petrol 159 (would probably have trouble getting under 10L/100km) - in which case, the diesel 2.4 comes out quite good.
I suspect if economy is important you'll be better off with the 1.9, but otherwise get the 2.4 for that 'power edge'. I learned here today that the later ones (210bhp) have better power delivery.
When I've driven a couple of 2.4s, they seemed initially sluggish, but the power available in the mid range and for high-speed cruising is huge. It's really quite fast and effortless, and the Japanese automatic trans (6 speed) suits it well.
When I drove a 2.2 petrol 159, it felt like a lighter and more responsive car at low speed, but the power delivery had no great surprises in store and it seemed to perform at about the level of my old 156 Twinspark (2.0, 150bhp). 156 is a smaller car, of course. People that have attempted to tune the 2.2 seem to be reporting the standard power as closer to 160, not the claimed 185, and while that's 'adequate', I'd be looking for a bit more.
Reliability-wise it seems there are fewer cambelt problems (on the 2.4) than there are timing chain problems (on the 2.2/3.2 petrols) and nobody's mentioned the 1.9 cambelt at all. Diesels appear to need some EGR maintenance/modification but it sounds like nothing too unreliable. Certainly it all seems quite different to the annual suspension rebuilds needed on my 156.