Free! It's free! The Sims 2 is free! I don't really know what more to say. The Sims 2 is free on Origin. You'll get all its expansions and add-on packs too. For free. Because it's free. It's all free.
I mean, the technical explanation is that EA have retired support for The Sims 2 and as a parting gift gave everyone who owned it on Origin an upgrade to the all-inclusive Ultimate Edition, but didn't have an easy way to give that to disc owners too, so they've just tossed a free code onto the Internet. But in short: The Sims 2 Ultimate Edition is free on Origin.
Basically, what you need to do is redeem the product code "I-LOVE-THE-SIMS". You can do that on the Origin site or through the Origin client and you'll get the whole lot. Yes, Origin is required but surely no one would even consider grumbling about that when all this loveliness is going free?
The Ultimate Edition includes The Sims 2's 8 expansions, adding everything from pets and holidays to seasonal weather and witchcraft, and 10 Stuff packs, small collections of items. Once that would have cost innumerable squillions of pounds, and even today it'd still be over a hundred quid new.
Ta to reader Ross for the tip-off.