DA2 is nowhere near as good as Origins. The plot had some things going for it but it threw them all away in the end. Hawke is a reactive character, not a proactive one. Things happen TO Hawke, which is not a great way to do a video game. The time skips were counterproductive to the supposed "rise to power" storyline. Skipping the first year, where Hawke establishes him/herself was a terrible mistake. Instead they decided it was important for you to make money. You don't really get introduced to the Templar v Mage conflict until Act 2, so it's hard to call that the main theme of the game. The Arishok was great, as were Meredith and Orsino, until they ruined the latter two by making them both go crazy. There was no investigation into the red lyrium idol, the most interesting thing in the game. It could have worked as a subtle influence driving people's characteristics to the extreme, such as Bartrand's greed or Meredith's paranoia, but both of those characters went straight up crazy, which ruined Meredith.
Origins plot wasn't anything ground breaking but it was a classic Adventure plot and worked perfectly for what it wanted to do. The Warden becoming a Warden is reactive, but after Ostagar you take the helm and drive the plot forward.
The characters in Origins are far superior. Varric is the only DA2 character who isn't completely flat and boring. He is, however, no match for Morrigan. That said, despite the characters being individually dull in DA2, their interaction with each other is somehow awesome.
Combat is going to be personal preference, but I lean toward Origins. I like that they tried to speed up combat a bit and make it flashier, but they went too far and made it very cartoony, with characters flying around the battlefield. Origins combat had more grit and weight, even if it was a bit slow.
Legacy and Mark of the Assassin were the best parts of DA2.