The guys over at Rock, Paper, Shotgun have just completed a series of posts titled Gaming Made Me in which they list the four or five games that have had the greatest impact on their lives. Sounds fun, my turn! I'm going to do this a little differently though. Each game will be its own post.

Ultima OnlineI played UO fairly consistently from 1997 to around 2001, with a lengthy break somewhere in the middle of those years marking my transition from "Gunther" on the Great Lakes shard to "Thrim" on Catskills. But let's start at the beginning.
In the spring of 1997 I was 13 and UO had captured the imaginations of a friend and I. We had never played an MMORPG or MUD before, but were familiar enough with RPGs to be awestruck by the possibilities. We would spend every recess at the end of that school year in grade 7 discussing plans for the formation of a secret society. We would infiltrate guilds, rise to the highest ranks, then betray or manipulate them. I never got in to the beta, and I don't think my friend ever kept up with the game, but it occupied my thoughts for the next several months. When it was finally released in the fall I found myself with game in hand but no PC or internet. After school I would go to the public library and pore over the official website, reading about lore, skills, etc. After a couple of weeks I received my computer (the first that belonged to me and not a parent - Pentium 233, no 3D card) and this new thing called broadband cable internet.
There were bugs. The servers weren't reliable. There was lag. Player killing was rampant, in this hostile new world. I'm sure it was annoying at the time for a lot of people, but I just remember the wonder that comes with exploring a whole new world with real people. I remember the get rich quick schemes which often resulted in my death. The panic, relief, exhilaration, dismay that comes with being chased by a murderer and escaping - or not. 
I had a good friend who I had met in a chatroom called The Proud Lion, and we became lumberjacks and bowyers based out of Trinsic. We would gather wood from the forests outside the city, create bows, and sell them to the NPC merchants in town for a hefty profit. Our first major investment was a pack animal, so we could carry more lumber and maximize profits. My most vivid memory from this time, however, was not honest work (grinding? Funny, it didn't feel like that) but an afternoon's adventure in the dungeon Destard. Each city in Britannia was paired with a dungeon, and Destard was Trinsic's. It was also the most dangerous dungeon in Britannia, full of dragons. I had no combat skills to speak of at this point - both in terms of character skills and my grokking of combat mechanics - but other players were starting to develop theirs. The dungeon was littered with the corpses of players who had been sacrificed as their friends ran back to the entrance. I became a corpse robber. I got into the treasure chests too, of course, and loaded up on gems and other valuables, but the bodies of dead players were the real prize. I hid from dragons, died a few times, recovered my items, and finally found myself encumbered by the weight of loot. As I exited the dungeon a group of players were waiting. They knew what I had been doing, and likely also saw that I had been flagged a criminal for stealing from innocent corpses. I tried running but several magical spells slammed into me and that was that. I was annoyed, but not upset. I was aware of the risk of being a thief. In the end, now over 10 years later, it didn't matter whether I escaped with the loot or not. The experience itself is what counts. UO's ability to allow players to find their fortune however they choose is what counts.
Months, years passed. There are too many stories to go through. Towards the end of my stay on Great Lakes I found myself extremely bored with everything. A new game-wide quest involving a couple of employees roleplaying as villains attempting to bring about the apocalypse brought me to Kazola's Tavern outside Yew, where I made new friends with whom I attempted to solve this mystery before any of the other tens of thousands of players. An encounter with one of these cultists on the island of Moonglow is one of the most memorable PvP fights I have ever experienced. There were just three of us against a super-powered human-controlled villain. Our efforts had paid off, and we were rewarded with a personal, unique event. Later quest events would try to be inclusive, and attract hundreds of players. Disgusted, or perhaps just bored again, I quit. I would never forget how powerful personalized, unique content can be.
A little while later I was going through a bit of a pirate phase, fascinated by the history of the Golden Age of Piracy. I was also starting to regain interest in UO. Catskills was known as the roleplaying shard, and there just happened to be a guild (crew) called The United Pirates recruiting members. I created "Thrim" and joined up. It was my first real roleplaying experience and I loved every minute of it. We would talk out of character on ICQ but always with plenty o "Arr"s and "matey"s while in-game. Again, too many stories to list, but thankfully our Vice-Admiral and co-founder Hawkeye Pike was an obsessive chronicler. Screenshots and descriptions of many of the big United Pirate events can still be found on his Travelogues website, which I often visit for satisfying trips down memory lane. There is one story not on that website which I often pull out when I want to explain to someone what made UO so great, so important a game.
First, some background: When UO was being designed, Raph and the others didn't really understand how widely used instant messaging would be. To make instant communication possible between players on opposite sides of the world, they created "communication crystals". These could be linked together and transmit spoken text when turned on. For example, Player A's crystal is off and Player B's is on. Everything Player B says appears out of Player A's crystal, but not vice versa. If both are on, text is transmitted both ways. These could also be dropped on the ground and transmit everything said by anyone within the vicinity. Of course, these were completely useless and ignored by every single person who played the game because we all used ICQ (I still remember my 7 digits: 4635333) to communicate.
So by now I was fairly well established in The United Pirates. I had worked my way up to something like Quartermaster, third in rank behind Admiral Hook and Vice-Admiral Hawkeye. We were on one of our many excursions to plunder and pillage the town (player-owned) of some virtue-following guild we were at war with. There were maybe a half dozen pirates and one or two landlubbers who we made short work of. We trashed the public buildings as best we could, putting everything not "locked down" in disarray, and in the process I found some communication crystals. I was immediately struck with inspiration and turned one on and hid it under a table in their HQ. It could not be seen unless the table was moved. I kept the other one it was linked to and made sure it was off so conversation would only be transmitted one way - to us. As we sailed back to our base at the Red Skull Bay (pirates, remember, we preferred sailing over magic teleportation) we listened as the landlubbers gathered in their HQ and planned retaliation. They knew what we were like, and correctly assumed we would be hanging out in our tavern The Jolly Roger Inn drinking rum and congratulating each other on some good plundering. They would attack us at this moment. But we heard all of this. If the game accurately modeled sound waves I'm sure our laughter from the middle of the ocean would have reached them on the coast. We raced back, stocked up an Greater Explosion Potions, put Deadly Poison on our blades, and took up positions in the Jolly Roger Inn. Using the hide skill which we were all masters at, we became invisible unless stepped on or revealed through magic. And then we waited, each of us, spread across the world in front of our computers no doubt sharing huge grins. We let them come all the way into the tavern. Some of us were behind the bar. Other tables provided obstacles that blocked quick escape once our trap was sprung. The slaughter was complete, glorious, wonderful. We let them gather their belongings in shame and go back to their HQ. We heard them trying to figure out why we had been prepared. Then I guess someone noticed a table was out of place and discovered the active crystal under it. The transmissions stopped. We laughed and got drunk and planned our next adventure.
This was spontaneous. There was no "arena" where we went to fight. It was not a fair fight in any way. This kind of experience had not been designed. It is the very definition of emergent gameplay, emergent narrative. It was only made possible because UO had an enormous number of tools at the players' disposal. The moment to moment experience of playing UO was not defined and polished to provide entertainment to the greatest number of players with all their different styles of play. Players actually had freedom in this game, freedom to choose everything from how they made money to how they used their imaginations. I'm reminded of Clint Hocking's recent comment that it's not worth working in the medium if every player shares the same experience. If every player cries at the exact same moment, under the exact same circumstances, what's the point? Ultima Online didn't have scripted quests back then. Every emotion, every memory I have from my time in that game is unique to me and the close friends who shared it with me. I would probably not have any faith in the narrative potential of this medium and social, online play if it had not been for Ultima Online showing me first-hand what is possible. It has been over 10 years and EVE Online is perhaps the only game approaching what UO accomplished, but is unfortunately not nearly as accessible. Like a monk in the middle ages looking back at the writings of the Greeks, I'm aware of what is possible. I've seen it. We just need to rediscover that lost knowledge and experience, and maybe one day improve on it.