I didn't romance him, and found his entire character arc (if you want to call it that) forgettable and very disappointing. Maybe they had too many characters. Maybe they chose to funnel funds towards graphics and world-building and so character stories got cut. Who knows. But what we got, both with Cullen and all the other characters, pales in comparison to Fenris pacing up and down in his mansion, growling and agonizing over Danarius, or Isabela showing up at your house, desperately pleading for you to help her, then later running off, then later RETURNING, or helping Merrill stand up to her mother figure, helping or dissuading her against working on her dangerous pet project, having her snap at you and tell you to leave, helping her defeat the demon she thought she could control, then having to either put her down or help her defeat her own clan.
I mean, no, the story, the drama, the conflict just is not there. So, so sad.
While there was a huge lack in companion interaction (asking them questions, kissing them whenever we want etc) DA2 was certainly far more character driven than DAI, all of them were interwoven into the main plot in some way and all of them had opinions on the situation that they voiced frequently. That's what's lacking in DAI and I think that's largely in part due to the whole open world feel to the game. I also agree that having a larger cast seems to have watered down everyone's involvement, which is some ME2 also had a problem with, although the game itself wasn't open world so it was far less noticable.
For me DA:O got it right when it came to companion interaction and involvement, flaws aside it done a good job of balancing out actual interaction with the protagonist (asking questions, initimate interaction etc) with the companions personal involvement with the main plot(s) itself. In regards to all 3 games DAI feels the least personal/intimate in terms of group bonding/dynamic and protagonist/companion/advisor interaction and dynamic, again I feel this is down to the open world/MMO approach they've taken.
What i'd love is if they put out a DLC that just added in more companion/advisor content in general, dialogue that was cut, scenes of the companions and advisors interacting with each other (like they did in DA2), that sort of thing. It'll never happen though.