In retrospect, why didn't I quote? Anyway, in reply to The Virgo:
You can compare two completely different things. That is, after all, the only way we discover that they are different. Anyway, what's more important is that you can still decide which is a better game. One way, for example, is to judge the experience it will provide. In this case, Deus Ex provides a stable single player experience that is mostly well-designed and fun. Battlefield 3 provides a single player game that isn't worth paying money for, and a more thought-out and focused-on multiplayer game whose quality is basically on a rollercoaster and, as such, is completely subjective (namely, subjective to the player and each individual online match he or she plays) 100% of the time. Therefore, I'd argue that by all rights Deus Ex is a better game. However, that may or may not be the issue in the OP's decision. I think the issue which game the OP would enjoy more.
You can compare two completely different things. That is, after all, the only way we discover that they are different. Anyway, what's more important is that you can still decide which is a better game. One way, for example, is to judge the experience it will provide. In this case, Deus Ex provides a stable single player experience that is mostly well-designed and fun. Battlefield 3 provides a single player game that isn't worth paying money for, and a more thought-out and focused-on multiplayer game whose quality is basically on a rollercoaster and, as such, is completely subjective (namely, subjective to the player and each individual online match he or she plays) 100% of the time. Therefore, I'd argue that by all rights Deus Ex is a better game. However, that may or may not be the issue in the OP's decision. I think the issue which game the OP would enjoy more.