I have a 2001 156,1.8 Sportivo. The only thing that went wrong (so far anyway) is the alarm stopped unarming which cost €39 to recode, and I just changed a speedo bulb.
Cam belt at 36K,Variator (except 1.6 model) and water pump while the belt is off.
Front wishbones are weak.
Some Twin sparks can consume oil so check levels every 7 - 10 days.
Crap dealer network and labour prices are the biggest Alfa faults, and of course the fact that people that never owned one "know" they're unreliable.
Its so much car for your money. Drive another car in the same class and it wont compare.