Been meaning to post a few thoughts since I finished my first rushed-get-to-know-the-game playthrough, but eh... on my 3rd (canon) playthrough now so yea 
I was a bit worried before the game came out, especially about Dorian. Gay characters are practically non-existent in the gaming industry (and the "invisible" ones are tiring for me - reffering to the ones you don't know they're gay, but the devs come in and tell you "yea yea they're gay, but it's just a part..." and some bs after) so I was worried how well he was going to be portrayed and whatnot.
Then the game came out and I was simply speechless at how amazing he is. I mean the writing is incredible, the voice acting, the animations... everything just comes together in one impressive package (pun intended). He just feels so real it's shocking. He has flaws, but he's trying to better himself. He's damaged by what happened with his father, but he didn't let it break him. He's trying to connect with people and open dialogue instead of falling on stereotypes and preconceptions (I think he tries to "find common ground" with all the other companions, if I remember his banter correctly and in most cases he succeeds).
Having a character with such a lovely personality and so clearly outlined with a few dialogue lines is really impressive. Top notch writing.
Personally I adore him. I tend to gravitate towards sarcastic in general, but mix that with smarts, charm, character and personality depth, a beautiful appearance... and I'm done
(all in one is so rare lol). He's my favorite companion in all Bioware games by far, and obviously my default... actually my only LI
3 playthroughs and it's him everytime... I'm not even flirting now with others haha (did it the first time with Cullen and a bit with Bull, and I liked Cullen's reaction; on Bull I'll get back in a bit).
Now about his pairing with the Bull. No. Just no. I understand why they added it, it's basically fan service, but the way Bull is written just makes their relationship horrifying for me. I know bdsm adepts (actually they're really just sadists who try to deny it - the ones like Bull) have all this little speeches about getting to know yourself by letting go of control and similar nonsense to justify it and/or make it seem ok, but it's all just bull (pun intended again). You just met the guy and you know what he needs? No. This also comes with a very irritating condescending attitude (which they nailed perfectly in Bull's dialogue, and makes it even more disgusting for me). Examples: the comment about topping from the bottom, his "mageboy" comment and the general attitude. What bugs me the most is Dorian is (as I understand the character) too smart to go for somehing like this. A one nighter, sure, no problem. A longer term thing? No way. Now if they address this in a dlc it would be fantastic. Something along the lines of "yea we parted ways... we wanted different things"... or more to the point Dorian saying something like "I don't want someone telling me what I need like I'm a child", which is exactly what Bull is doing (to the Inquisitor as well in the romance from what I've seen on utube - "it would disrespect you to do otherwise" lol... no Bull, you're just afraid to bottom and are a sadist... just have the b*lls to admit it
- quote is not accurate, but that's the idea when you talk to him about it). As a side note I love how Solas demolishes Bull's so-called arguments about the Qun, about everything really.
Anywho, back to how amazing Dorian is... he's amazing
(nod to the Rift mage specialization trainer who must be one of the funniest characters ever lol)
His party banter is also hilarious for most parts (when it's not it's not really his fault, with trying to open a line of communication and whatnot). His dialogue with Solas and Varric are best imo. Witty snark all over.
Finally, his romance arc was just beautiful, and his sex scene one of the best (I haven't watched all of them though so I can't really say... well actually, diplomacy aside, you get to see Dorian naked... there's not even a competition for me lol).
As soon as a hotfix comes for the mess that was Patch 2 (what is it with Bioware and the number 2? really now - DA2... yea, ME2... yea... Patch 2... yea...
), going back to finishing my main playthrough, human mage, in love with Dorian, and going for sexy times with him everytime he's in Skyhold haha (I do wish you actually had that possibility lol, in addition to just a quick smooch but I head cannon that that is actually the after* kiss... )
Cheers!