In Ultima Online years ago, if you committed a murder or criminal action in town, you could be killed by guards. If you committed a criminal action out of town, you could be freely attacked by anyone with zero consequences for ~5 minutes...if you died, anyone could loot your body and take everything you had on you. If you committed a murder and were reported by the victim, you gain a short term and a long term murder count and become a criminal (and therefore can be attacked by anyone) for 5 minutes but you could loot everything they had on them. Once you got 5 long term murder counts, you became a murderer and were freely attackable by anyone at any time for any reason without consequences to them, you could not return to any town, and the only access to your bank was in a lawless town frequented by other murderers or groups of innocents coming to raid.
The only way to get rid of short and long term murder counts was play time. Short term murder counts take 8 hours of play time to drop one and, if you had more than 5 short term murders and died, resurrecting would cause you to incur 'stat loss' whereby you lose 33% of your accumulated skills (which sucks a vast array of ballsacks...like..so many ballsacks). Long term murder counts take 40 HOURS of PLAY TIME to remove ONE. Essentially you had two options; (1) become a murderer and hide out for a day or two while you worked off some short terms and one long term to get below the threshold of 5 and become an 'innocent' again (or at least get below 5 short terms so you're rid of stat loss and you can play, even though everyone can attack you wherever you go) or (2) go balls to the wall and become a straight up pk.
That was probably the best game I have ever played (before it was fucked by Origin and EA) and I haven't seen anything like it since. I think the specific reason for this was the balance of the approach but the fact that you still had the freedom to do what you wanted, as you should in any sandbox style game (especially MMOs). All modern games try to find that balance but fail so miserably because the only drawback to death in subsequent games is a temporary resurrection sickness or having to run all that way again or looking like an idiot. No one really cares about dying because nothing really happens when you die and nothing really happens when you successfully evade pursuit or beat your attacker. Even more importantly was the fact that even people playing as innocents could still have a bad day and rampage a bit without screwing things up forever. That and the fact that if you talked shit, you better plant your ass in town or be able to back yourself up because people with only a couple murder accounts will kill your ass for being a dick.
Living the life of the roving pk required that you were extremely clever, very skilled, and played way more UO than any human should ever have. Ultimately most people had multiple characters and at least one of them was red (murderers were indicated by the normally 'blue' name over your head becoming 'red'). I played initially as an innocent while building my character and getting used to the game but the first time I was chased down by a group of pks I felt that adrenaline rush and, even though I lost everything, it was unlike any experience in any game before or even after. By the time I was done with UO, I had played on several different servers but my favorite was Napa Valley...I had 3200 murders and a 7.5mil gold bounty on my head. 1280 of those were a single 15 day killing spree after GMs had placed rocks in front of my house to let it decay because they didn't like me. I didn't hack, I didn't cheat - I just killed the shit out of everyone I could and the GMs hated the complaints...so I gave them some work to do. By the end of the spree I had resurrected with stat loss 3 times but that completely fucked my character so I had a friend turn my head in for a bounty, gave him 2.5 mil, and sold the other 5 mil on eBay for $140 bucks (when gold was worth something in the game).