I started when I was nine years old, at a friend's birthday party. He'd snuck into his older brother's room and made it out with some of his gaming books - namely, a copy of Expedition to Barrier Peaks and most of a Fiend Folio. All he knew was that it was some kind of game, and that his brother and his friends really liked it and yelled at him whenever he tried to get into the room if they were playing it. The books got passed around but, well, none of them actually told you how to play the game, so most everyone lost interest and walked away.
Everyone except me - I read through and, with my limited understanding of the rules and a set of Yahtzee dice, we set off for glory. It was, as you can guess, a complete and utter bodge of a game, with me making stuff up on the fly, and while I don't recall much of the sessions, I remember skipping whole rooms because I just didn't understand what they were telling me to do. At the third session, his brother found us playing and, rather than being angry, was elated and let me borrow his books for a weekend. I basically memorized them.
In the ensuing decades, I ran and played a bunch of games, but in the end, I've always come back to Dungeons and Dragons, and I've played every edition up to 4th edition, and until picking up 13th Age most often played 3.5 or Pathfinder.
A friend told me about 13th Age and loaned the book to me and after only a few pages I was pretty well hooked. It did a lot of things I wanted in an f20* game, while having a few flaws that seemed easy enough to file off. After playing for the better part of two years, here's my rundown. First are the things that 13th Age keeps from previous editions of the game. Second are the things that 13th Age doesn't do that some people might find integral to their gameplay. Third are things that 13th Age really innovates, either coming up with new mechanics whole-cloth, or incorporates from other games in a unique way. Last are positives and negatives.
Things 13th Age Keeps
The basic tropes
Y'know, elves, trolls, orcs, fighters, barbarians, druids, that kind of thing. You're definitely playing in a D&D world if you're playing from the resources in the 13th Age book.
You roll a 20-sided die for almost everything, adding or subtracting numbers and comparing them against a target number to determine success. More on this in the innovations section, but it's nice that they keep this basic mechanic in place because it's familiar and it works.
Of all the 4th edition mechanics, this was probably my favourite, from a player perspective. Instead of having healing spells that add some random number of hit points to your character and can be mechanized so hard that you can literally have practically infinite healing in a stick, you have a set number of times in a day that you can roll a few dice to get back hit points, and then you either rest or, well, die. There are spells and items that can effect this, but it sets a pretty hard limit on PC resources.
Simple stat blocks for monsters
Most monsters can be written up on the front of a 3 x 5 card and I've yet to find one that can't fit on both sides. This is similar to 4th edition monster presentation, although the mechanics are quite different.
Straightforward character abilities
Another adaptation of 4th edition design strategy, with the exception of a handful of highly narrative spells or abilities, most character abilities can be summed up in a single sentence on a character sheet or, again, a 3x5 card.
Things 13th Age Doesn't Do
Everything has a stat block
3.5 and Pathfinder have a lot to recommend them, but the feeling that I needed to know the Wisdom score of ever random peasant farmer wasn't one of the pluses.
The golf club effect
In 3.5 and, to a slightly lesser extent, Pathfinder, at a certain point a martial character could expect to keep three or four weapons on them at a time in order to actually be effective at attacking all enemy types. That isn't an issue in 13th Age - you can have the same weapon at the start of the game as at the end, without much effect on how difficult it is to hurt stuff.
Technically, this isn't true. Treasure, including gold, is still part of the game, but there are no rules for how to spend it or how expensive things are or any of that. My players are currently at epic level, and I think the richest of them has about a thousand gold pieces - it just doesn't come up that much in the game's mechanics and you can step right past it if you want.
Tactical map combat
There's no counting squares, no facing, no real need for miniatures. We still use them fairly often, because while you don't use an actual combat, whether you're in melee combat or not does matter for the use of some abilities, and moving around in combat can still create problems for your character, but it's not represented in blocks of formal movement around a map.
Things 13th Age InnovatesBackgrounds
Instead of skills that are tied to a specific ability that may or may not ever be used (seriously, whose idea was it to have "Use Rope" as a discrete skill), 13th Age characters have backgrounds, descriptions of what they did before adventuring or the things that lead them to become adventurers. Backgrounds in my current campaign vary from the concrete, like "Seer" and "Bodyguard," to the more abstract, like "Pyrophile."
In the first round of combat, nothing much special happens. In the second round, you get a +1 on all attacks. In round three, that's +2, scaling up to +6 by round seven, should things get that dire. This is best represented by having a six-sided die on the table, the escalation die. This has several effects. First, it discourages PCs from using their strongest attack in the first round. They'll usually only have one chance at that, and if they try it when they have the least chance of it succeeding a couple of times, they'll soon learn to wait a round or two. Second, it builds a nice sense of mania into the combat. By the time you get up to +4 on the escalation die, your PCs will hit so easily that they'll start coming up with crazy ideas for attacks and in-combat actions that really just make the game fun.
The mechanics are really a synthesis of several different f20 games, but in the end, you roll a 1d20 and determine the effect, and then maybe roll your damage dice. Which - get this - you get one damage die per level. Yes, a barbarian with greataxe is rolling 10d12 for damage at 10th level, but don't worry, the monsters keep up with you.
The game comes with 13 of them already written out for you, but there are various builds out there - basically, icons are characters, concepts or beings that your character is somehow connected to. It's essentially a mechanic that tells you when the big movers and shakers in the campaign world do something that impacts your character. I really like this because I tend to create these complex, deep campaign worlds and then forget to have the players actually interact with them. This mechanic takes that out of my hands and puts it in the PC's hands.
This is a frickin' DM's paradise. You roll 1d20 and you rarely, if ever roll damage or really make a decision on what the monster does, mechanically. Damage happens, status effects happen, and as a DM you're free to build up cool and interesting characters without worrying about whether the dice will let you do it. It's really quite wonderful. (My favourite is building encounters that degrade as they go on - someone uses a fire attack, the environment gradually burns down around them inflicting damage, causing issues with ranged attacks due to smoke, collapsing floors to make movement difficult, etc.)
One Unique Thing
This might be my favourite thing about the game - every single PC has something about them that makes them special, different from everyone else in the game. This can seem sort of silly, like my rainbow-coloured half-orc, but even then, it has utility in the game. Gorvak, the rainbow-colored half-orc is kind of a legend at this point, and specifically because he stands out in a crowd. You never have to question whether or not he's in a fight, and tons of people know him because of it. Everyone else has their own special thing, too, and all of them get use in the game, some more than others.
Positives and Negatives
+ Fantastic bestiary - It is, quite simply, the bestiary by which I judge all other bestiaries, with sections on ecology and use in game that just make them sing.
+ Fights are simple - I like theater of the mind combat, and the lack of a combat map can actually make fights more strategic, just in a different way.
+ Improvisation - In the last session, I improvised an epic-level fight on the fly. Try that in 4th edition.
+ Light narrative structure - With Backgrounds, Icons and the One Unique Thing, I can tell stories with my players without requiring them to take a writing course.
+ Straightforward play - We've never taken more than a minute and a half to look up a rule.
- DMs can roll a lot of dice - While you only roll a single die for each monster, you can easily have 15 different monsters in a fight - using an online dice roller evens this out, though.
- Fights can take a lot of creativity - Where the monster mechanics are so simple, unless you do something really interesting with the encounters, they can feel kind of same-y.
- Treasure doesn't matter - I grew up basing my games off of the information in a module, and playing lots of Final Fantasy, and not having long lists of game-impacting magic items feels wrong somehow.
* This is the term some people use to refer to games that operate off of the rolling of a 20-sided die, but may not use the actual Wizards of the Coast d20 mechanics.