-The
gap between F2P and P2P in 5.3 was
as low as it ever was: level 20 gears got a +4 ilvl boost per slot, improving stats in bgs, and stats are calculated as if they're 24s (no new abilities), allowing one to actually reach spell hit cap vs 24s. This is still present in 5.4, even if mouseover stats are bugged (mouseover stats on items in-slot are not correct. Such mouseovers are correct if items are in bags or out-of-slot though. Ex: naga gloves while giving 7 agi 7 stam outside bgs now gives 8 agi 8 stam in bgs, even if mouseover stats say otherwise).
With 5.4 however,
P2Ps got access to new, more powerful enchants (mongoose, elemental force, etc, even though they're "scaled" down [scaled down, but same scaling at levels 1-60, only improves beyond 60. One would hope blizz changes that]), and several classes-strong-enough-to-not-need-damage-buffs got dmg buffs (primarily rogues and hunters, and arms warriors).
-Compared to cata,
class abilities/utilities have changed, some classes gained more ultity and others lost some (rogues lost the most imho. Outside stealth they're as kitable as cata warriors in-combat, nevermind their damage). If you want to see the abilities/utilies each class has now, look no further than
here [talents and other abilities] (some changes also applied to 24s, like
Shadow Priests).
-All races now have 2 min. free-from-ccs-insignias instead of 5 min.
...Hunters and rogues rule the bracket.
Classes with utilities may still survive and beat a rogue (1v1) if they can kite and survive a rogue's opener.
Hunters... yah.
Almost cata damage, with slightly more utilities.
Almost like cata though, heals (from most healer specs) in comps help counteract those FOTMs (despite 5.4s buff to battle fatigue, nerfing all heals), nevermind some absurd FOTM P2P bursts.