I agree with you OP. I don't hate the game as much as I find it extremely underwhelming.
Your point about the side-quests is spot on. DA:I feels and plays more like Guild Wars 2 than it does a Dragon Age game. Also, the Hinterlands is a ****** terrible starting area. Other zones have grinding and fetch quests too, but the Hinterlands is by far the worst of them.
The storyline was very meh. Corypheus being the main villain was AWFUL. I didn't really hate him as much as I found him an annoyance. I didn't really feel the impact of what he was about to do, and didn't know enough about his motivations to care about what he wanted to get. All I cared about was stopping him from destroying the world. When I first found out that the main villain in the game was 'The Elder One' I thought it would introduce some new unanswered questions about the lore, possibly The Black City, the Blight, or some other supremely interesting, unknown, stuff. I read the leaked achievement list and knew that Corypheus was in the game, but even without that it would be far too easy to guess (that black silhouette in the prologue is not inconspicuous at all). They could've expanded more on Corypheus' role as an ancient magister and what happened in The Black City, not necessarily providing clear answers, but making Corypheus an interesting character beyond being a simple "baddie". Also, I thought that the main boss battle would be an epic showdown in the Fade, or even the Black City itself, which would be pretty cool. At the end what I did was walk up to Corypheus and destroy him. The Hinterlands dragon who I killed while being 6 levels ahead was a tougher fight than Corypheus...
PC controls are clunky and uncomfortable. No excuse about it, the worst thing being is that BioWare claimed they made the game for PC. It allows you to only have 8 skills in your toolbar, veiled under the explanation that it's for "strategic reasons", but is there any reason for this decision other than the game being played multiplayer on consoles? They could have added the toolbar to 10 or 12 skills and preserved the "strategic" element.
I remember reading interviews from the devs where they claimed that the main storyline alone would take about 50-60 hours to complete, and 100+ hours on a "completionist playthrough". I'm about 55~ hours in and I completed the game. I finished every optional area (I did not embark on the area where you get the quest to eradicate the Venatori near The Western Approach, and assuming that is a big optional area, that is the only one I didn't finish) to about 90%, every rift in those areas are closed, most landmarks are found, most quests are done, and I'm missing only 6 shards to open the last set of doors to Solasan. It's safe to say that the main storyline does not take 50+ hours to finish, since I just finished the game and approximately 70-75% of my time was spent on side-quests and optional content.
This is a pretty petty complaint, but why exactly does the game still have a stat system? It's basically very redundant at this point. We can't put our points into stats anymore upon leveling up, and there is literally no numbers to tell us what the stats do, what damage we do per auto attack, so why even have the stats? Why not just say "Damage: 200", "Health: 500", "Mana: 200". It's just much easier and less confusing, because if I add an amulet of 10+ Cunning to Sera, I have no idea what it does and I have no idea what it adds. I can only hope it boosted her stats well enough to make her a bit stronger than she was before. Saying it adds +30 damage instead of +20 Cunning would clarify things a lot more.
While I don't care that much for the quality of romances, and I would be the last person to whine about them as the game's biggest flaw, I recall again the devs saying that the romances are "fulfilling" (paraphrased). I can only speak for a Cassandra romance, which I found to be very rudimentary and basic in terms of actual romance interaction and importance. I flirted with her 2-3 times, she sees through it, I read some poetry and then we hook up. After that there is some dialogue which comes from romantic endearment, or Cassandra in some situations acting/reacting appropriately to what you would expect someone you're involved with to act, but that's basically it. Again, can only speak for the Cassandra romance, although I have a hard time imagining that the other romances are much better.
Honestly, I just finished the game and I had to vent. I watched every possible video there was to watch before the game was released and was beyond hyped. I remember seeing the first announcement following the survey leak in September 2012. Have been waiting for the game since, and I am a huge fan of the previous games, even if I did not think DA2 was a wholly excellent and stimulating game. At first I thought maybe it was just my unrealistic hype bringing me down, but after playing the game I can safely say that it has some pretty nasty issues that shouldn't be there.
I'm contemplating on whether or not I should do a second playthrough at all. It's honestly very draining and exhausting to go through all those areas once again, and the main storyline is not good enough to make up for it. One reason I bought the game was because I expected to do multiple playthroughs, as I did with the last 2 games, which as of now I don't know whether I'll be doing them.