Do you think video games have gotten too easy? Do you think quick-saves are a crime against all gamedom?
If so, Irrational Games doesn't want Bioshock Infinite to disappoint you. They're adding a special setting, "1999 Mode", that forces players to make extra, gameplay decisions that cannot be changed.
For starters, in a "1999" game, players will be forced to choose an upgrade specialization: Whatever style of play you planned on using better work for you, because you won't be allowed to deviate from that specialization or re-spec your character at any time.
On top of that, "1999 Mode" does away with checkpoints. In you die and cannot be revived, you'll find yourself staring at a "Game Over" screen. In other words, you have to be very careful about managing your resources, because can't start over if you use too many healing items or ammo.
Luckily, "1999 Mode" is an independent setting, so you if you like a challenge but also like to checkpoints, you can just play on hard. Conversely, interested players who are might balk at the idea of having to make tough choices can choose give it a try on a lower difficulty to counter-balance the weightiness of their decisions.
