Crazy isn't it? I would never have guessed that one day I would need to force myself to play a Bioware game. In some way's I still can't believe it. 
I have to admit. There's a lot of things I like about DA:I, but also a lot of things I strongly dislike. I'm even more divided in my mind about it than I was about DA:2, because, with the right restriction-unlocking mods, graphical overhauls etc. DA:2 turns into actually a pretty good game, albeit one horribly flawed in the final act in terms of nonsensical plot and railroading.
But I digress.... I've completed Inquisition exactly once, and thus far played only Jaws of Hakkon DLC.
LIke you, Inquisition is the only Bioware game I ever played that caused me to lose interest part-way through, and lose the will to continue. This malaise began to creep in shortly after the extreme disappointment of Wicked Hearts and Wicked Minds, and by the time I got to the brain-numbing slog of Hissing Wastes, (which caused all my remaining will to play to simply evaporate, and the game to feel like a chore) I'd had enough and took a break, where I went off to play other games. This had never happened with any other Bioware title.
Eventually I picked it up again, and completed Inquisition, and continuing the main plot helped greatly - I'd not rushed the main plot, and only done it in small stages, spending lengthy periods doing side quests in different zones in between main plot sections.
If I ever play Inquisition again, and I'm sure I will at some stage, I intend to pretty-much ignore all the needless rubbish that (I feel) sucked the pace and life from the experience - shard collections, landmarks, item collections etc. focusing only upon the main quest, and such side quests as I can be bothered to complete at the time. That means no more wasting hours of time in the Forbidden Oasis, futilely trying to scrambling up impassable slopes to reach something glinting at the top.. let it glint! No more running around trying to put a landmark marker on the top of a ramshackle building with no obvious entrance.. and no more farming for materials.
I like the main plot very much, and I like the characters, or at least most of them. I find the combat very dull, awkward and clunky when compared to DA:O and DA:2, and the eight slot limit on spells/abilities sucks all the fun out of building and speccing your character. I don't get the "Oh Wow! Look at that spell further down the tree!.. can't bloody wait to get that!" sense of excitement I got from both previous games; and I always felt somewhat detached from the action in Inquisition, it always felt like I was observing everything third hand, rather than actively participating - the emotional ties are nowhere near as strong.
Still it's a decent enough game, and I'm glad I at least finished it. Probably the best thing you can do is grit your teeth, accept the flaws, and finish it, knowing that there will be times when it seems a slog, but working through those sections with perseverance and patience. At least that way you'll know how the story ends.