Eh...well...my last car was a Volvo 850 with the straight 5. They are pretty stout, but they have their quirks and problems like anything else. The Volvo's don't have a PCV system, at least the 850 didn't. It has a flame trap, which has to be periodically cleaned or it will foul, plug up, and cause the internal crankcase pressure to build. This will then cause seals to start popping, most likely the rear main. These are not easy or cheap to replace. Other than that it's a decent motor. Don't expect to much in the way of power unless it has the turbo, which I believe the S40's have the low pressure setup, correct? My daughter could accelerate faster on her bike than my N/A 850. Transmissions were not great in the 850's either, but that was largely Volvos fault. They marketed the car as having tranny fluid that was good for the life of the vehicle, yet they were using the same DexIII fluid as everyone else. As a result, I'd say roughly 1/3 of the 850's out there had to have their boxes replaced by 100K miles, at $1800 to $2400 a pop. Mine was starting to slip at 110K when I gave the car to my dad, and I had changed the fluid at 90K when I bought it. Was to late, the damage had already been done.
Last thing though, the newer Volvos are fiendishly complex. Having owned a modern Volvo I won't buy another one newer than what I had. I was talking to a guy who is a tech at my local Volvo dealership and he said the eletrical systems in the new cars as so insanely complex that they often have to get someone to come in from Volvo to figure out how to fix them. Not trying to discourage you, just be prepared that they are not exactly considered cheap cars to own or maintain, but they are nice.