There's a growing trend among gamers of my generation to download and play, usually on emulation programs, the games we grew up playing. Star Wars Rebellion is one example of this, though there are many others. Typically these games are classified as "Abandonware" because it is believed that their developers have abandoned the selling of these games, and so do not have a claim on the copyright for those games, allowing them to be downloaded for free without concerns about being sued.
While the legality of this issue has been in question for some time, and I do not believe it has been decided in a court, this is indeed illegal at this time. Video Games are considered "Intellectual Property" and the copyright expires 100 years after the game is published. In other words, a long time from now, even for the first games. Like illegally downloaded music, you run the risk if you download a game, even abandonware.
The crux of the issue is that it is unlikely that most companies will pursue legal actions. Some developers, like Sierra, do not exist as corporate entities anymore, and others have been bought out and absorbed by bigger companies. This may mean their copyrights are owned by non-existent corporate entities. It may also mean that they are owned by giants that have whole teams of lawyers waiting to pounce on you. The net result is that it is illegal, but whether or not you will get sued over it is in the air.
Just some thoughts.