Re: General opinion
IMHO Volvo Penta is the Cadillac of drives. Volvo was the first to the market with a mass produced stern drive.
I always LOVE this "who was first" argument.........which of course, doesn't really mean mean much...... It's like a "Chicken-Egg" (which came first?) scenario.
If you REALLY want to know who first "invented" the stern drive you have to look at the history of Kiekhaefer Corporation............whose engineers really invented the thing........Volvo didn't "invent" a stern drive....... they sort of "bought" the (AVC) design and brought the Aquamatic to market "first"

.
They certainly did improve on what the Kiekhaefer people originally designed......
Make no mistake, It all started at Kiekhaefer though.....You can read all about it in the following article:
The information below comes from patents and the book, Iron Fist, by Rodengen. It is a biography of the life of Carl Kiekhaefer the founder of Mercury Marine. Chapter 26 (pages 360 to 379) is titled, "The Great Stern Drive Conspiracy."
Stern Drive The Invention of the Stern Drive
Now should you buy a used Volvo Penta engine/drive combo boat?
If it's a really old one, No........... for same reason I wouldn't buy an old Mercruiser MC-1, TRS, MC-II , OMC Stringer, Cobra etc......... They're old, obsolete and parts are scarce.
If you're talking about a newer Volvo SX drive, (mid 90's and newer) Absolutely. There's nothing wrong with them!
EXCEPT: If you like to scrounge used parts on Ebay, Craigslist, Boat Trader etc........
For example, you will find approx 3 times more new and used Mercruiser engine/drive parts on ebay (boat parts) in any search than you will find for Volvo ( a moment ago it was 28,xxx : 10,xxx)
New parts are approx the same price if you're a smart shopper. (probably with some exceptions)
When I started my search (Fall 2006) here in the NW (Seattle/Puget Sound) area for a replacement engine and drive for my 87 Four Winns Liberator (in my sig), Over about a 6-month period, I found several complete "Fanbelt-prop" SBC/BBC Alpha/Bravo I II III combinations for about $4500-$8500............ I searched Seattle Puget Sound and Portland Or.
I even priced new engines and drives (in 2006)
The Volvo Penta big-block Duo-Prop combination was almost exactly the same cash price (NOT Incl install) as the Mercruiser BBC/Bravo III .........it was similar with the smaller engine/drive re-power combos.
I did NOT find any complete used Volvo Penta engine/drive combinations for sale in the same areas during the same time period........If I had, I probably would have bought one. I wanted a Volvo BBC DUO-Prop combo to put in the boat.
ymmv...
Rick