For me on either side the sentiment can be summarized by moments of “holy shit. That just happened…”

Plans going perfect, plans going awry, shocking acts of RNG, excellent performances of narrative or improv.

For years now i thought the details and the world building behind the campaigns is the most fun part, at least for me. After now three to four years building a world, without having my players play even one session in this world. I don’t deem my world ready yet. I think it’s never gonna be played. Its to much fun just creating the world. I don’t want my player find a loophole while playing and me having to fix it mid game with a not as perfect solution as it could be.

I love creating the bones of a world or a situation, then seeing how the party interpret, contribute, and react to it, then reacting to their decisions for the next session.

Also sometimes, making traps and BBEG plans for them then being able to pull it off (and watching like a proud parent as they successfully get out of the situation)

Not strictly a DnD player (Pathfinder and World of Darkness mainly) I love the “creatively appropriating” ideas and concepts from other media, figuring out what makes different genres work and pulling everything together into an awesome narrative. I love it when my players get into their characters.

My current PF campaign is heavily Destiny inspired, so I’m pulling all kinds of ideas from the lore and the game itself and reworking them into a more strictly fantasy setting.

Three years ago I wrote some notes regarding the lore and background of the world I placed my players in. Now they’re invested and actually hunting down the villain I added only as a background.

Nothing is as good as players being invested and exploring the world well past my initial ideas.

I love when my players get deeply immersed in a scenario I created and engage with all of the NPCs and create a story we’ll tell each other for years.

I love when players start putting clues/lore together and figuring things out.

It shows they care about my setting and they’ve been paying attention.

Both as a player and a DM is theorising and imagining ways that different scenarios would go. Both tactical combat and social encounters. Even if the ideal circunstances don’t come up and my characters is not that broken or my players predicable enough for this to happen, It feels so good to make a decent build that makes sense or cool encounters.

DM here, mine is a bit vague and cheesy but whatever. Favourite part is seeing how excited my friends get when something cool happens! Whether it’s pulling out a spicy combat encounter, or they connect the clues of some big plot point, or they pull off something heroic and/or disastrous in game and we all know it’s unforgettable.

Being a DM feels a bit like hosting a party (except less overwhelming). It feels like giving gifts to my friends in the form of a fantasy world. It’s highly fulfilling, and we end up weaving many joyful memories together.

(Also hello from a fellow Curse of Strahd DM!)

I enjoy helping others experience the first time wonder of discovery, even after years of playing. It’s why I play in a custom setting and regularly create new monsters, spells, subclasses, and magic items. So many people crave that moment of first contact, and I love to help them find it.

On the DM side of that, when there are new things for the players to find, I get to stretch the creative muscles that I thought I had lost for years. I get to challenge myself to create new, interesting, and balanced experience to offer up for my table.

When I first started DMing, I focused a lot on maintaining a captivating pace at the table, and also had a few story beats that I wanted to hit, and kind of nudge the players towards. This meant I was able to pull off some gratifying one-shots, or short arcs, which I thoroughly enjoyed, but longer adventures started to become too stressful to properly maintain. Especially if there is a larger connecting world or lore in place beforehand, that felt more constricting as the campaign went on.
Practically it felt like being a filmmaker and making every session sensational. And when it worked, it felt awesome. If a session did not land properly however, I felt quite discouraged afterwards.

Then I discovered: hey, I want to be surprised as much myself by the events as the players at my table. I don’t want them to follow my pre-existing story beats. Rather, I want to be an impartial arbiter and just see how the players react, and especially interact.
Want to kill a key NPC? Sure, you can try, and if you manage to do it, the world will react accordingly.

Three things I employed to make every session much more enjoyable for myself:

• Adventure Design. I build adventures and campaigns “bottom up” (instead of top-down, where you do a lot of worldbuilding before play starts). Basically it means I have smaller sandboxes, with a few hooks, that might not even be backed up by anything yet, and just see what the players engage with and what sticks. Check out this Matthew Colville on Youtube, that explains it way better than I could.
• Powerful Tools. I like giving the players meaningful powers and abilities, that are powerful, but also have some drawbacks. Not talking about the default “+1" magical items, but more like “you are invisible while you play this flute loud enough” or “With this ring you can breath under water, but you dry up if you don’t submerse yourself in water once a day.” And as soon as they earn such abilities, I just let them use it. Bypass substantial parts of the adventure? Well OK, you earned it - even if it’s hard in the moment to accept as a DM, I err on the side of just allowing it, because it feels awesome as a player to just be allowed using ones tools successfully.
• Random Tables. I was very reluctant to use it at the table, because I did not wanted to drag the pace down and maybe “misinterpret” or tank the pace of a session. Sometimes I even rolled on random tables before a session, to “prepare properly”. But as soon as I committed to trying using random tables during a session, I noticed, that these sometimes quite improvised elements, caused the most fun on the table overall. And I just like being surprised by these twists and turns they might offer, how I can interpret them, and especially how the players react. And more often than not, they cannot even tell afterwards, what sprung from a random table, and what was planned beforehand.

tl;dr being surprised by the twists and turns in the narrative I did not expect myself

I’m like you, I love making homebrew items and monsters to throw at my party in equal measurements I also really enjoy creating lore and reasons why things are happening in the setting. I’ve been meaning to try a module so I can practice working within an existing story framework more.

As a player I love any time we actually get to play, quite a lot of time spent away from the table unfortunately.

DM here. The biggest thing for me is when the players get emotionally engaged to the story and the beats. They fell actual hatred for the BBEG. They get so excited about a reveal that they all can’t talk for a minute. Something happens in game, and half the players are having a chat in the Discord in character, outside of game time. The reactions from the players are so rewarding.

The next best is when they come up with a solution to a problem in the game that I hadn’t even considered. It’s kind of fun to have to just say “OK. Hang on a minute. I was totally not prepared for y’all to try that, so I’m going to need to figure out what they impact of that is.” The players always get really excited about that; I think they love to stump me.

As a DM, my favourite part is the worldbuilding. I love figuring out how the setting works, what its history is and who the prominent people are. I do worldbuilding as a solitary activity sometimes, but having an audience makes it better and having a participatory audience is best. I ran a year-long campaign I called the “zero-prep campaign” where I didn’t do much or any preparation ahead of each session, letting the party’s decisions guide things and frantically filling in the universe around them as they went, and I managed to produce one of my most cohesive and fun settings yet.

As a player, it’s similar but much smaller scale - I focus on building my character. I try to settle in to his or her skin, get to know them, figure out what they think about and how they’d react to various situations. The character is on a road I don’t know the ultimate destination for and I am keen to find out.