Kill Switch definitely needs more polish, more replay value, and just more content in general but it’s still a decent game.
Rainbow Six: Vegas is good on it’s own merits but does not represent what the series is known for. It’s a cover based shooter with lite tactical mechanics. No real thinking required.
Even today, Max Payne 3 has some of the best gunplay you will ever see in a video game. This is a must-play for fans of action games.