It seems like everyone feels the same way about the 1750 TBi in the 159.
I think it is a great engine... although the economy is pretty awful (worse than the 07 plate 220 bhp BMW 325i Coupe that I had before the 159).
The one thing that really stands out about the engine is the "mid range"... very much like a diesel in that respect. I wish it was a little higher revving... and didn't start feeling a little flat as you reach aroun 5000 rpm.
The engine note is OK... but not great. And, I find that if I try to pull away without sufficient revs (i.e. at least 1500rpm) it tends to bog down (although I am assuming that is because there is hardly any torque below that point in the rev range.
On balance, I prefer it to the engine I had in the BMW... although I do miss being able to make use of the higher end of the rev range... but, having said that, I use the low down torque a lot more in regular daily driving...