I've mentioned this before, but I think a large part has to do with what BioWare-game-players do in a BioWare game.
I think it's safe to say that the majority are "100%-completionist" types, i.e. we talk to EVERYONE and we scour the Journal and Codex for EVERY LAST QUEST, DIALOGUE, and XP.
Nothing wrong with that, and I freely admit that that's the way I play them.
But trying to do that in Inquisition is a pretty tall order. I have a save file that I keep around in case Dragon Age: Tevinter can use it.
Human male mage; I have close to 200 hours into that save over a period of 6-8 months, playing it on-off, it's my "canon" playthrough where everything is just so; all the dialogue options, companion quests, major decisions, all the way down to what I'm wearing and what abilities I have.
I have over 500 power, Inquisition is rank 20 (max level), I am level 27 (max level), and I have enough crafting resources to make weapons for my entire group of companions using nothing but Dragon Bone, Dragon Scales, and Dragon Webbing.
With Mastercrafts.
I have everyone's armor tinted just so, and everyone has optimal accessories based on their skill-sets.
I could go on.
Long story short, it's big, and it's long.
But technically speaking, it's not 100%. The Requisition system is designed to never run out, i.e. I have a few Requisitions that I can't complete because the enemies that drop the items (Decorative Gems or some such) no longer appear, so they stay in my Journal, forever unfulfilled, and the completionist in me is irked by that, just a little.
I think part of the discomfort is that Inquisition requires a different mind-set from previous entries and from the Mass Effect trilogy. The "BioWare classic" is semi-linear in nature, like a train follows the tracks, but there will be different sets of tracks, which regardless all lead to the same station.
Here we have something akin to an open area and we're in an off-road vehicle with enough gas to get from Point A to Point B, and a map with some fuel locations.
Trying to do EVERYTHING is possible, but such an extensive process isn't necessary to advance the plot.
You can literally pick and choose what you want to do to gain Power to unlock new areas and/or main missions.
I have a female elf playthrough in the works (I'm interested in seeing the "Solasmancer" arc for myself), and I'm not fussing over the nitty-gritty, and I find it's a much faster experience.
I'm skipping entire areas, because it's either out of the way or it's not part of a quest, unless it's dragons.
Always fight the dragons.
To summarize, BioWare veterans are accustomed to a certain "flavor" of experiences, whereas Inquisition has us consider other "flavors", and I think it does so very well, considering what they had to work with and what they had to work around. Dragon Age 2 was meant to be much bigger than it turned out to be, largely because fans gave it such a hard time, much of what was originally planned for that made it's way into Inquisition.
Adding in the fact that there are NINE different companions, each with one of the specializations that fits into their back-story, and then having individual character arcs for each one...
It's an incredible thing.
If someone is complaining that the game takes too long, it's because you're trying to apply "old" gaming knowledge to a "new" game.
Don't get me wrong, I have nothing against that mindset, nor do I wish to imply that it's "outdated" or "lame", it just doesn't sync-up to what Inquisition offers.
Ironically enough, the LESS you focus on 100%, the more you get out of it.
Dragon Age: Inquisition is every bit deserving of it's Game of the Year status and whatnot, you just need to adjust your mindset.