Personally I just hope a large and diverse book gets added back in like origins. I liked the idea behind DA2's ability to add extra effects to existing spells to reduce redundancies, such as walking bomb. But the trees in DA2 felt small and restrictive. So much so that optimum choices tended to stand out and all the party's mages more or less had the same stuff beyond their specialisations.
Whereas in origins I could have 3 mages in my party and they would often all have different powers with their own combos. For me Wynne would be using healing and glyphs. Morrigan was using Fire, Ice and sleep/fear/nightmare spells. And my warden was using hexes, drains, lightning and telekinetic. Thus even if you had mages using the same tree it was still possible for them to have different abilities.
Well i think DAO was skill-overkill - especially for Warriors. I always ended up with about lvl 25 and having the whole toolbar filled with Icons of skills, but mostly i only used a third constantly.
So in DA2 i was glad about having les sklills but make them upgradeable - even though the upgrade-system lacks innovation... like having to chose between 2 upgrades (which both change the wy the skill works) and you can only pick one. And by doing this 2 or 3 times the spell/skill changes completly.
area effect - firestorm (ball turning into a pillar of fire throwing smaller firebolts around)
/ \ wrecking ball (like a lava-ball steamrolling anything in its way and burn it)
larger fireball
/ \ / implosion (enemies getting sucked towards the center of the spell)
/ adding explosion to fire damage - knock off (explosion causing close enemies getting knocked to the ground)
Fireball
\ homing projectiles(high accuracy) - incinerate (continuous flame damage)
\ / \ bouncing off (causing collateral damage)
barrage of smaller fireballs
\
meteor shower(low accuracy bit wide range) - continuous rain(extend duration)
\ hard impact (weaken fire-damage but add earth-damage through groundspikes)
And I think it was sad, that the crosseffect-system of spells didn't return (likely the most innovative thing about origins).