As a player...
It wasn't long after I joined a group of my, then, room-mate and several of his friends who had been playing together, on and off, for quite a long time.
My, then, room-mate was running the group through the Standing Stones module, and had adapted certain aspects of it to fit within a sub-plot started by one of the other DM's in the rotation. There was a moment where we met somebody very old, and the DM tied this NPC in with some of our character's backstories. To tie it in with the sub-plot some relatives of some of the PC's (including mine) had left some items for us with this very old man. And he spoke to us about the people who had left the items for us with him and he handed them out.
It was very poignant, cinematic, and cool.
There were other great moments, like when the Dwarven Paladin was almost killed by sixteen demonic lemures, or when my extremely chaotic rogue/cleric realized that she was a bad influence on said Dwarven Paladin, or when just about anybody did just about anything... But I'll go with that as my number one pick for a moment as a player.
In the unfamiliar role of DM:
This year has been significant in that I gave sitting behind the screen a go. Now I had co-written and co-ran White Wolf LARPs for a number of years back in the day... But sit down D&D is a whole other animal, and I was very intimidated. My first cool moment was when I realized that the guys were actually having fun and, while I was very inexperienced, I didn't completely suck.
I quickly discovered that my one true (Rat-Bastardy) joy as a DM was luring the PC's into held actions and AoOs in combat.
My crowning achievement came when I had an NPC baddie run away from the aforementioned Dwarven Paladin. The NPC fled through a secret door, across a room, and then through a regular door, which she left open and, unbeknownst to the PC, hid behind it. The Paladin gave chase, and passed through the second door, thus incurring an AoO from the NPC who attacked him... By attempting to slam the door on him... I critted.
I critted the Paladin with a door.
So I look up at our most knowledgeable rules person and I say, "What sort of damage does a door do?" There was no answer, they all just looked at me. So after a moment of blinking I said, "I'm just going to say it's a heavy mace and call it a day." And they said, "Sounds like a plan."
In being a gamer and getting older:
I recently moved into a new apartment. And, as a early Christmas gift, my folks decided that they would get me a dining table and chairs. Now, it's just me in this apartment, and the dining area isn't that big, so the table had to be a smallish size. But I definitely wanted it to be expandable, because I figured on eventually hosting family holidays once in a while... And of course, it had to be able to fit at least five other people and our giant battle mat if the guys were going to come over for D&D...
So we go to Ikea and start looking at tables, and I was having a hard time picking a table. One looked cool but wasn't expandable, one was expandable but I didn't like how it looked, one looked nice and was expandable but was smaller then I wanted even when the leaf was in... Then my Dad calls Mom and I over and says that he found one that he likes.
If you have an Ikea (store or catalogue) near you it's the Bjorna (with an umlat over the "o") style table. (I don't think it's listed on the website.) It's a light wood butcher block style that's rectangular. So we slide open the table to see how long it would be with the leaf in and, get this, the leaf is attached to the frame of the table. So when you open it, the leaf folds out from underneath... And when you pull out the leaf, the table can seat seven people with plenty of elbow room. I had to work to keep my cool, it was the ultimate table, it had all three F's;
Form, Function, and Fit the giant battle mat.
Somebody once told me that you know when you have become an adult because you get excited over something like a kitchen table... But what if you're excited because the kitchen table is perfect for D&D?
So of course that's the table we got. I had my family over and we had Thanksgiving on the new table to break it in. But then the big day comes when I had the guys over for the first time to game. They show up with the aforementioned Giant Battle Mat, I open up the table, unfold the leaf, and they were all like, "Wow, this is the perfect gaming table." and I grinned, like an idiot, and I was like, "I know!"
Bjorna table from Ikea
With an umlaut over the "O".