Research and Development is a puzzle-centric mod for Half-Life 2: Episode Two featuring an unarmed player but plenty of violent mayhem.
This is one of- no, THE best mod I have ever played. I loved every single aspect of it! The form of indirect combat used was sublime, and the puzzles were challenging, yet very very fun! One of my favorite parts was getting to actually build Mr. Whirly, the game's unique junkyard-styled vehicle. Nearly every aspect of the game was perfect. The only thing lacking in any way is the replayability, but that suffers in many puzzle games.
To sum it all up, this game is the best mixture of the action and puzzle genres since Half-Life 2 itself! Even though I hate bugging game developers, I certainly do want to see another installment of this thriller in the future!