Serious Sam: A Random Encounter.
An interesting take on the franchise, instead of just running and shooting, the game is built a bit like an old RPG such as the Final Fantasy series. It's got a world map and battles are sort of turn based but with action... it's somewhat hard to explain, so just have a look at some gameplay footage: www.youtube.com/watch.
Anyway, I'm quite liking the game, and I recommend you have a look at it. You can buy the game for $4.49 €3.59 £3.59 on Steam.