Seasons passes are designed to save gamers money, by offering a discounted price for DLC, which is all paid for upfront or in bulk. Unfortunately, the cost of said deal is often quite high all by itself.
Case in point: it has been reported by multiple outlets that the season pass for Aliens: Colonial Marines will cost a whopping $30. Yes, that's the same price of an entire game, brand new.
The season pass covers four pieces of downloadable content, which would otherwise cost $10. So yes, you are saving money.
The downloadable content is expected to be released throughout this summer and will contain additionals for the campaign, new maps, new modes, character customization, and more.
On the bright side, at least the game does not require an online pass, which would prohibit or greatly restrict online play unless one has a code that comes in new copies of the game (or which must be purchased if the game is second hand). Those are far worse than season passes.