Choice in attributes is probably one of the biggest illusions in DA. You could work against it, but that would always gimp your character for most of the game.
1) You always had to stick to your main attribute or not have enough attack to hit anyone.
2) Non-main stats were decent at best, very limited in DAO, and hard to itemize for in DAO and DA2.
3) You had to always stick to your main attribute to unlock skills (in DAO) and gear requirements ( DAO + DA2)
4) It always ends up being a burden rather than "fun" after you hit the high mark.
5) Gear always become useless compared to innate stats (unless modded or hacked).
In DAI you can add stats to whatever you want without worrying about keeping up with some requirement. It's totally viable to ignore dexterity on your rogue and pump it all on cunning for massive crits. Damage is more tied to weapons, so your tank can pump con and still hit like a truck from the get-go. There are new stats from guard break to flanking bonus to crit damage. Previously mages could rarely make effective crit builds. Who doesn't like spell crits? Most satisfying **** ever.
Also, stats from gear and passives are roughly equal throughout the game, allowing you to spec your character in any way you want.
Consider the crafting stats to be the "distributable" stats of DAI really. You never had the option in previous games.
Regarding sustainables, they were not removed. They were simply transformed into active sustains(blocks typically) and passive sustains (literally passives).
Sustains were almost useless half the time in DAO (I'm looking at you warrior and archer trees) and impossible to stack in practice in DA2. They were also largely an "activate and forget".
In DAI you have to actively toggle the sustains in order to get the effect. This leads to a more reactive style of combat which can make playing the game more fun for your character.
In previous games, most passives were simply %modifiers to the character's stats. In DAI, most passives can completely alter how you approach and perform in combat since they add "if's to your gameplay.
Some add % damage if you're at a certain height above the target. Always move your archer to higher ground.
Others add %damage if your enemy is knocked down. Synergizing by making your allies take knockdown abilities becomes a fun possibility.
Some increase mana regen if you stand still. Winter's Stillness weaving is pretty fun at low levels. etc...
The gameplay is simply different. Things were changed rather than outright removed, and in my opinion for the better.
I would like the return of "if" statements for tactics. That's probably one thing that is missing in DAI.