The 240 was a solid, simple and dependable troublefree car that was easy to maintain and repair when need be. The S80 is the exact opposite: It's very problematic (never buy a '99 or '00), costs big $$$s to repair, maintain, many repairs require going to dealer as the Vadis PC is required for diagnostics, software, etc. The car will never last like the 240s without first emptying your bank account. Those who own them/like them describe it as a love/hate relationship as the car IS nice to drive WHEN everything's working.
I'd keep, buy, maintain older RWD 200s/700s/940s (not 960s) anyday over thinking about buying an S80 unless you don't mind costly, annoying, never-ending, repeat problems that require several trips to your local dealer. Most people don't enjoy that, I wouldn't either.
The '02s on up are better than earlier years so if you really want one, buy a newer S80. Don't expect ANY new Volvo to be like an older "good" RWD car like a 240, 740, 940 (best RWDs IMO).