Well this is a pretty good deal.
Steam is currently selling a Deus Ex Collection featuring...
— Deus Ex: Game of the Year Edition — Deus Ex: Human Revoluion — Deus Ex: Invisible War — Deus Ex: The Fall
All for $6.59. Yeah, that's worthwhile, especially if you haven't had the chance to play the series.
You can also pick them up individually if that's your bag. Every single game in the series in 80% off.