If you want a good single player shooter, the last really great one I played was COD MW4.
A bit old now, but much better than the later games in the series. Also the Battlefield Bad Company games were not bad. And I second the Borderlands games, either one or two.
RTS games, are subjective, and unfortunately not made as often as shooters now, but there are many older ones such as the Age of Empires series, Battle for Middle Earth series, and Supreme Commander and SC Forged alliance that are really good. And of course there is always classic Starcraft and the new Wings of Liberty and Hots.
For action/adventure, hack and slash, have to recommend Titan Quest and Immortal Throne along with Torchlight 1 and 2.