Killing spree: Easy, with a bit of luck you can get one in seconds with an amp or deemer. But still..... they feel pretty good. If you get one of these, people will start to keep an eye on you.
Rampage: Aha, now this is where it starts to get good, you've proved your not just lucky, you have skill too
Most people will take note if you get one of these, and probably avoid you if possible.
Dominating: These are impressive, at this stage people will stop avoiding you, and try to take you down. Your best off trying to fight defensively now.
Unstoppable: To me, this is the coolest sounding spree. It marks you as 1337, and by now people will be throwing themselves at you to try and take you down. By this stage, you'll probably be getting very defensive, even to the point of being a coward to prevent the lose of your spree.
Godlike: The big daddy, at this stage most people will stop and either think "wow, what a guy", or "damnit, that punks dead!" Most people dont live much longer than this, cos its a unwritten rule that all godlike players will probably lag shortly afterwards, and find themself facing a wall with 5 and a half rockets loaded up