For instance, as you gain levels, your attack rolls and defense rating go up automatically. And so do your hit points and the amount of damage you do. If they'd only increased one set or the other (sort of like how D&D Next's bounded accuracy only increases HP and damage), the system would feel smoother.
In practice it still runs smoothly for a couple of reasons:
The first and most important of which is that levels 1-10 spans all the way from the start of Adventurer Tier to the end of Epic Tier. That's 30 levels worth of 4E or 20-odd levels of 3.X. Broader leveling windows are counter-balanced by the "Incremental Advancement" mechanic, but you still only get 9 bumps to your Attack and Damage stats over the broadest potential adventuring career. Compare that to the worst possible BAB progression in 3rd Edition and you still have less +1's to manage.
The second factor comes along the same lines - no Christmas Tree characters like the other editions of D&D assumed. You see equipment-based AC or Attack bonuses of only +1 per Tier. Compare that with the standard payload under 3.X/OGL: +1 to hit and damage and +1d6 elemental damage per "plus" per every 3-4 levels or so is the bog standard equipment increment for the Grogs. Add on Power Attack / Sneak Attack and multi-attack and options for increased critical threat range and you've got a bizarre, item-and-feat dependent matrix of damage algorithms that still pale in comparison to spells. In 13th Age it is way more important who is wielding a weapon than what weapon you are swinging.
And they do tend to write out abilities more like 4e powers rather than actual narrative things that just need some game mechanics to model them.
One of the awesome, recurring themes of the whole 13th Age book is just that: "Here's a specific mechanic with broad applications and an open-ended narrative. Go nuts." Seriously, just read the entry under the Swashbuckler talent for the Rogue or Cantrip Mastery under the Wizard. They aren't kidding.
What exactly does it mean that you roll even vs. odd on an attack? (A left-handed swing vs. a right-handed one, perhaps?)
"Natural Even" and "Natural Odd" die rolls refer to the number on the dice before adding any modifiers. These are basically coin-flip results without having to roll any extra dice. Flexible attacks let you roll to hit and then decide whether to activate an applicable feature to that result like.
"Naturally Even Hit" is an attack roll that (after all bonuses and penalties) scores a hit and the physical number on the D20 you rolled was 2,4,6,8,10,12,14,16,18,20.
The only exception to that is the Half-Elf. His racial power specifically let's him fudge the Natural Result of a d20 roll by -1.
- Marty Lund