Friday night, I played in an online game of 13th Age, which is a D20 game. That is: it is a clone of Dungeons & Dragons 3.5 with added rules. (Pathfinder is another one of those. During the era of D&D 4th edition and until the release of D&D 5th edition, it ruled the roost and in it's own turn spawned a whole set of games that are compatible with it.)
The group of players was excellent, but the game felt very flat to me. I mean, there's plenty to like there: every character has 'one unique thing', there's powers and spells that trigger during or outside of battle, there are 'Icons' which are the movers and shakers of the setting and the characters have positive, conflicted or negative relationships with them, etcetera. Everything for a cool game in a rich setting.
And yet, it was a bit of a slog. Perhaps this was due to us not being familiar with the system or perhaps this was due to not having played with everyone in the group before -- but I don't think it's that. It is that D20 combat (and the scenario was basically a set of combats strung together) is a slog. You can't do cool things at low level because you don't have those abilities. And in fact, D20 combat is not about doing cool things, but all about damage output per round and killing things through a million papercuts. A siege troll took maybe ten combined hits to bring down.
Contrast this with, say, The Hobbit where a single bowman can bring down a dragon in a single shot. Sure, a single bowman of outstanding ability, but still. You can't do that in D&D, it just doesn't model fiction like that.
But Dungeon World does. I completely agree with this assessment by Weem: Dungeon World ruined things.
I really like the people I played with Friday, and would game with them again without any reservations. And yet I kind of feel horrible that I didn't like the game and at the same time thought that this set-up could make such a cool scenario for Dungeon World...