Well, it appears you have already found your answer. Regardless, I will confirm that the '99 S80 is an utter toilet. Mind you the 2.9 engine originated in 1995 and was well suited to its original application e.g. rear wheel drive sedan. That said, I owned a 1998 V90 and it was a phenominal car owed in large part to the rear wheel drive. I sold it w/ 175k on the clock and it was still running extremely strong with relatively minimal issues. The 2000 S80 2.9 is arguably much better (than the '99) and I have a number of friends who currently own/have had them and all in all could not fault them. (I would seek out a '97/'98 S/V 90 or a '00 S70 SE - these are boxy .) Otherwise, the newer the model, the better it gets. As another poster mentioned run away from the T6 version (twin turbo) as that is the biggest toilet of them all. Lastly, Volvo incorporated the 5cyl Turbo into the 2004 S80 and on. That is an excellent drivetrain and can also be found in the s60,v70,xc70 and xc90.
And no the brand is nothing like it was in the mid 80s to mid 90s.