I've read in several previews that the range of the radar around a Spartan in multiplayer has been reduced. I don't have any good way of quantifying that, but it certainly seems to be true to me.

In particular, on Valhalla there are two rock outcroppings on either side of the stream where players often like to perch with ranged weapons like a turret, sniper, or laser. Often there's a lot of activity far away that they are paying attention to, and more than a few times I've run right up to such a player from behind and assassinated them if there's no one covering their back. It's also happened to me quite a few times as well.

I have a feeling that the radar may have lost most of its usefulness in many situations if this is the case. It can tell you if an enemy is nearby but on a different level, but doesn't indicate whether it is higher or lower, so this is of little use. Out in the open, you'll see a player long before he or she ever shows up on radar, so it's only good for detecting someone outside of your line of sight. If the range is so short, however, that it's routinely possible to run (not sneak) up to players and melee them before they have a chance to register an enemy on the radar, it makes me wonder if it shouldn't be either removed entirely, given a greater range, or provide additional information, such as the elevation of a target.