I don't find it that overtuned, but I can see why people would think that. Once we figured out the mechanics, the fights seemed pretty easy. However, I think healers would probably disagree with me, as there does seem to be a LOT of damage going out on every fight. Garrotes on Moroes and sacred ground on maiden cause a lot of healer strain.
It requires DPS to use their healing cooldowns and such, which hasn't typically been necessary in a lot of 5 man content.
What I believe is happening is that Blizzard is testing us on whether we will like 5 man "raid" content. This is certainly not your typical mythic+0, but since it drops mounts and much better gear than mythics, I don't think we would expect it to be like +0.
The biggest problem is the run backs of course. I anticipate that will be corrected by/on next Tuesday. It's a trivial thing to fix. They just make you spawn at X place instead of Y, when Z conditions are met (AKA bosses are killed).
Regarding itemization, I think that's to be expected. Recall that because the ilevel starts out so much higher than other 5 mans, there is as much higher chance at you getting 860 870 880 gear than from M+0 or LFR. I think once people get an item like that, they will change their tune.
Recall that when an item warforges, it flips a coin to see whether to increase 5 ilevels, then flips another, etc. The result is that it becomes exponentially harder to get 895 proc from an 840 base than an 855 base. Three extra coin flips is the difference between (just for argument's sake) .04% chance (840->895) and a .4% chance (855->895) (using a 50% chance at each 5 ilevel bracket). That's 10x more likely to see an 895 from Kara than from Mythic+0 dungeon.