I can comment only on 9spd 105 (2003). Hubs, crankset, front derailleur and brakes well-engineered (pads don't last long). Chain, cluster adequate. Rear derailleur suffers from cheapo completely unsealed jockey wheel bearings, which rust and grind with a sniff of water, but can readily be replaced. Brifters a bit uncertain and (my ones at least) inclined to jam completely so that one can neither shift up nor down-always unjammable after a bit of fiddling but undesirable in heavy traffic (I replaced them with DA). Bottom bracket starting to grind a little after about 9000km, while hubs are pristine. 105 pedals not very durable; axles badly pitted after ~7-8000km.
Obviously, the current gruppo has changed quite a lot but some of these comments may still be relevant.