Research and Development is a puzzle-centric mod for Half-Life 2: Episode Two featuring an unarmed player but plenty of violent mayhem.
this game is simply the most amazing mod there ever was in the puzzle genre! I will even go so far as to say it is better than portal! Valve really needs to hire the people that made this mod, the only problem I had was the driving at the end, but thats because I've never been good at video game driving with a keyboard :P
Absolutely fantastic, manages to bring fresh and new gameplay to half life 2 whilst making it still feel very much like a Half Life game!
I hope Valve look to this mod for inspiration when making puzzles for episode 3, rather than just reusing that see-saw puzzle they made us do 20 times already :P