[speculation]
All dice rolls are now dynamic (1d20) attack vs. a static defense.
An "attack" is 1d20 + 1/2 char level + relevant ability mod + Class Bonus + Misc Bonuses
A "defense" is 10 + 1/2 char level + relevant ability mod + Class Bonus + Misc Bonuses
"attacks" includes melee attacks, ranged attacks, skill checks, spellcasting, talents (smite), and other d20 rolls (initiative, for example)
"defenses" include AC, Fort, Reflex, and Will.
So (making up some class bonuses) a 1st level fighter (+5 class) attacks a first level wizard (+2 class)
The fighter rolls 1d20, adds 1/2 level (0 or 1, depending on rounding, we'll go with 0) his class bonus (+5) and his str (+3, 16 str). His roll is 12, so his total is 18.
The wizard has 10 + 1/2 level (0), class (+2) and dex (+2, 14 dex) for a total of 14. He's hit.
Now, the wizard acts and casts sleep on the fighter.
The wizard rolls 1d20, adds his spellcasting class mod (+5) +1/2 level (0) and his int mod (for being a wizard, 16 int, +3 mod). His roll is 8, so his total is 16.
The fighter defends with his will save, 10 + 1/2 level (0) + class mod (0) + wis mod (1, 12 wis) +2 for Iron Will (his feat). for a total of 13. Not good enough, he's napping now.
Whats great is that this exact round will play out exactly the same (EERU) with both characters being at level 20. Simply replace the +0 Class level bonus for (+10). However, when fighting foes of unequal strength, higher level PCs have a strong advantage of lower level foes, and vice versa. So level really does become a large factor in how strong a PC is. (of course; talents, feats, and magical items can further skew the math in favor of one person or another, but the baseline is a lot more constant that 3x)