Some freeware stuff off the top of my head:

Cave Story if you haven’t played it already. It is the best platformer evar.

Within A Deep Forest is relaxing and fun, as are Nifflas’ other creations on that website.

Lyle in Cube Sector is a pretty rad Metroidvania platformer.

Ancient Domains of Mystery if you can handle it. This game is epic, but incredibly difficult to get into.

Finally, get The Spirit Engine if you want a good, free, straightforward RPG. It delivers on all fronts with excellent graphics, music, dialogue and a unique combat system. (There’s a sequel to it coming out in the near future that will be commercial, but the original is still free and as good as ever.)