More details:
Right now, there are two maps: Rome and Castel Gandolfo. Personally, I prefer the castle. There are 3-4 levels of height on each, and certain areas in the castle have 3. Both maps are a pretty decent size.
As you level up, you get abilities, and unlock characters. I'm level 14 right now. I have a superspeed ability, smoke bombs, the hidden gun, a disguise ability, and a morph ability. You can only have two at once (they're assigned to you L2 and R2 buttons). Disguise turns you into another character. Morph turns everyone in a small radius into YOUR character, so if someone's after you, it'll cause confusion. As you get points for eluding, it's useful. Your abilities can be used and then they reset in a minute. I'm about to get perks, too (I assume, assigned to L1 and R1), but I'm not 100% sure what they do. You can have two profile sets with different abilitites, and you can switch them during the game. I've been using morph and superspeed.
I also get 300 points if I make 3 kills in a row without losing a contract or getting killed, and if I lose 3 in a row my locator gets extra sensitive.
You can also stun your attacker, but I think I've been able to do it once; it's really hard. However, my best kill (750 points) came after someone stunned the guy I was after. I essentially ran up and kicked him in the head.
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A basic chase kill is worth 100.
As of last night, there were ~40k people on. I was ranked about 3k on kills (I've spent 6hours on), but my killed/kill ratio isn't great.