I'm loving it. I have about 35 hours logged now, and I'm still not done. It is astounding just how much stuff is in this game. I've also heard that they plan to add even more. Good Lord... I'm sorely tempted to buy a second copy of this on Steam. Not because I have a problem with this version, but becasue this game is worth much more than just $15. If I could go back in time and back this on kickstarter, I would. In fact, if you know of a way to donate to Cherry directly, let me know, 'cause I will do it.
And if you just got the wall jump, you have a LONG way to go.
I don't know about any of the kickstarter art, so I can't compare directly. I'll check it out though. But as far as "bug horror" goes, without spoiling anything, the botton and bottom left areas of the world map are a nightmare. I hope it meets your expectations :) I have zero desire to go there again.
You can see the art here
. Early concept art went more for a giger-esque aesthetic and the game was called "Hungry Bug" at that stage, but changed over time into what Hollow Knight is now. I actually stumbled across the lower area you mentioned by accident after I got my wall-jump. There's a secret passage that lets you access it from above and I kept overlooking the exit, so I explored the whole area in my attempt to leave. Tensest part of the game so far! I'm now exploring the rest of the city after getting my ground stomp, before I go off to see how I can reach the dreamers.
I also think that the game is too cheap. This is a full-blooded Metroidvania with added Dark Souls flavour, at a price that suggests a nice but short indie game. If you do buy another copy then I'd say follow Marioface5's suggestion and do a giveaway on GOG - generate some 'buzz' (get it? eh? eh?). The game could do with some user-generated hype. ;)
Also, looking at some of the kickstarter updates, while carefully dodging spoilers, told me that we can at the least expect Hornet as a playable character, several more bosses, a few more dungeons and a new village. Looking at how well they're living up to their stretchgoals made me bit bummed out that they didn't reach their higher stretch-goals for even more content. :/ The way they're implementing backer content in general is also really good and not disruptive at all - loved the glade.