I went back and replayed DA:2 after playing Inquisition. I also went back and played DA:O again. There were a few things in the Keep I wanted to check out.
DA:2 is unique in the sense that Hawke is really a villain, and you can see that in replaying. You're trapped. Your choice is do what is going to turn out badly or turn off the game. Just about everything you did in DA:2 had a bad outcome.
Everything there bad happened because of you and your companions, over which you have very little influence.
Varric is the one with the expedition. Without you asking Anders for the maps and setting them up with Bartrand, that expedition wouldn't have happened. No Red lyrium, no Meredith.
The Arishok is there because of Isabella. He wouldn't have had to stay or wouldn't have chosen to fight if she hadn't taken the Relic.
Replaying shows you were even more screwed than you thought, and you pretty much knew you were screwed.
It's dark, it's gritty, but I think it also has some of the best writing and the most interesting companions.
You could also look at it as setting history in motion. You provided for disaster, while possibly trying to prevent disaster. You can't alter Meredith, Anders, Isabella or the Arishok.
If you replay not in the sense that you're a hero, but that you are doing your best and still a victim of circumstance and likely the bad guy as a result...I think it's entirely worth replaying.
I think the Arishok is the best bad guy that they wrote in the series. It still makes me laugh and I just have to adjust to the idea that I wasn't the person driving events, events were driving me.
You're screwed, but your companion backstories are amazing. You're not the Scooby Gang solving problems, you're the Scooby Gang being and making problems.