I MUCH prefer DAO combat over DA2 combat.
On speed:
DAO was trying to be more traditional, with a more gritty and realistic look/feel.
Though they did not get the weapon speed animations right. The 2H warrior is intolerable for me to play as my PC, though I could have one in the party. No weapon in the real world swings that slow. It is just absurdly slow. I had no other issues with the animations.
DA2 OTOH gives up any sense of realistic look/feel, it is just some kind of weird super hero action game, where all the characters teleport, leap 40 feet, or run 300 MPH, and vomit lots of color.
DAI: I just watched a Movie compilation, but it looks a lot closer to the DA2 side of things.
On difficulty:
DA2 is easier. I tried I quick first few levels of both recently. I did DA2 first, then DAO.
DAO is much tougher starting out(level 1-7, which is as far as I got). Some of the reason is, you can't just pump your main stat. Shield Warriors need Dex, Dual Weaponer need Dex, Rogues potentially need a mix of Str(armor)/Dex/Cun. So you often can't wear gear, or you can't get skills. There are tradeoffs, that make you build less uber. Then there is the need to position rogues to use them, and archery is kind of weak. There is friendly fire of Normal/Hard (I killed party members with my own fireball more than once).
In DA2, A rogue gets almost everything from Dex. Hit/Damage/equip, likewise warrior only need strength for their gear/skills... Rogues do more straight up damage, and most of the rogue skills support archery, and there is no need to position to attack.
Almost everything is easier in DA2 and that is the point IMO. Make it easier and flashier.