I know this is an old article, but it's new to me. I have some more suggestions. Diablo I and II are great hack and slash games that kept me sane back in the day when they first came out and they are still fun to play. There's nothing like shooting something with an ice arrow and then shattering it with a sword. So fun. Neverwinter Nights I and II are the same way along with the original Baldur's Gate games.
You also have the first couple of game in The Witcher series. See how it all began. Those games are drm free and any updates they make to the games are always free to game owners forever. Bioshock worked the same way when they made the Enhanced editions of I and II. I got those free since I owned the first two and I believe you can play those on low spec systems. Playing Bioshock in surround sound is highly recommended, especially if you want to wake up you adult son who is trying to sleep all day. (I didn't do it on purpose but he came out of his room really annoyed from the sound of the Big Daddies walking. It's still amusing to this day, especially since it was an accident)
Then there is Vampire the Masquerade: Redemption and Bloodlines. I love both of those games and I had so much fun playing them. It's especially fun if you like to be stealthy when you make your kills as a vampire. Plus in Bloodlines you get to hack and do other fun things.
My most favorite of all though is Dragon Age: Origins and the original Mass Effect game. You should definitely be able to play those on lower end systems. I have hundreds of hours in both of those games just on the PC, and then hundreds more on the Xbox. That is how many times I replayed them. I love the characters, the story, everything. You may even be able to swing Dragon Age 2 and Mass Effect 2, they are older. I don't remember the specs but it was several builds ago for me and quite a few years ago.
There is also The Sims. People still play and mod 2, 3, and 4 so you can pick whichever fits
