Dominion is a card-based board game where you have to construct a deck to efficiently gain victory points before the game ends. I’m horribly hooked on the free (unofficial) online version of it. The rules are pretty simple but the game is very complex.
The “best” strategy varies depending on which combination of cards are available for that particular game. This is what makes Dominion extremely open ended. Varying the cards that are available can change the game dramatically.
Dominion is my favorite strategy-esque game at the moment. It’s like chess but less boring (way less thinking) and more open-ended.