I started getting into some old classic games that have been sitting at the back of the bookshelf for some time. Really old DOS games. Some of them need a little help to run under Windows (hell they often needed help to run under DOS), but if you are lucky, there is a Windows version already ported and ready to roll just waiting for you to download and start to reminisce.
There is a game I used to play on my old Commodore64 called Paradroid. This guy who also enjoyed the game released a free version of it that runs on Windows called FreeDroid. I spent ages playing it. It was just like playing it for the first time again, only with a mouse and keyboard instead of a one-button joystick.
A Chris Sawyer game from way back called Transport Tycoon Deluxe has been reborn in the open souce community with a multi-platform version called OpenTTD. Myself and a couple of mates have been playing with virtual toy trains until the wee hours of the morning.