I loved the game. It made full use of the Dying Earth setting to deliver a slew of strange concepts, which I found extremely stimulating. The writing was generally of a very high calibre, and even the descriptive text I found to be a cut above almost anything else in the RPG genre (c f Pillars of Eternity where a lot of the descriptive text and worldbuilding is awwwwwfffuuullly boring and should never have made it into a finished game - though it's a good game for other reasons). I liked the reactivity built into the interactions. I replayed Planescape Torment recently and something that bothered me was how there'd often be no recognition that you'd done or learnt something. For example, I'd be well into the Clerk's Ward, having done every quest I could, and still have the exact same conversation with Pox outside the Mortuary, asking who the Dustmen are and what they believe. From what McComb said in one of the streams, this may have been a casualty of technical problems with the engine. Numenera had excellent reactivity - if I'd learnt something related to one character or which might be relevant to a quest, I'd usually have an option to bring it up in conversation in NPC interactions. Consequently, it was very easy for me to look at the situation the Last Castoff was in, think 'How would I deal with this?' or 'What would I want to know if I were in the Castoff's position?' and explore the resultant avenues of inquiry.
It's probably fair to say I was most interested in the setting and writing behind the individual quests, which is where the game was strongest. Gene Wolfe's The Book of the New Sun is one of my favourite literary works of all time, and Jack Vance's Dying Earth isn't far off (honourable mention to Michael John Harrison's Viriconium - Harrison is, much like Wolfe, a technical writer par excellence). The thing I most would've wanted that the game didn't give? More! And by that, I don't mean that the game is short - I don't know exactly how long it took me; my recorded gameplay time is just under 43 hours, but I spent quite a bit of time with the game open in the background while I was doing other stuff, so I'd estimate I'm in the mid-30s for game time, which is not short. What I mean is I loved the world and quest writing so much, I'd love to have played a sprawling, Baldur's Gate 2 length game, seeing all of the weirdness that the Ninth World has to offer. But I understand this would be beyond budget and not worth the return on sales. Anyway, the game's flaws don't feel so significant to me.
I can see how they would turn someone else off the game, however. Combat was flawed, for example - not irredeemably bad, but with faults in execution such as the time taken for turns, and poor encounter design. The central storyline was also not great. It didn't feel like the game's primary antagonist related particularly well to the game's purported theme, nor was it well-developed. I think the inadequate attention paid to the Sorrow is probably the biggest failing of the game's writing. An additional area to the game, in which you explore a location related to the Sorrow's origins, would have done a lot to remedy this, even if it wouldn't have fixed the direct role of the Sorrow in the story's central conflict.
The Changing God was interesting and I thought dealt with well. Possibly more could have been done with him, but he's a concept which could be pushed in so many directions, and there's so much that could be done, that it'd be very hard to look at any particular use of him and say that that use exhausted his concept or executed it perfectly.
Some of the flaws other people experienced I did not find - for example, I liked the companions. Again, more could have been done with them, but what is there is not bad. The only one I did not care for too much was Tybir, who was simply too generic. He wasn't done badly, so that failing is no real knock on the game. I also liked the visuals. Sure, more animations would have been nice, particularly combat animations, but I thought the art style and colouring were vivid and evocative.
To summarise my view on Numenera, considered alone: I liked it a hell of a lot, and it's probably my favourite RPG since the Witcher 3, and before that... Vampire Bloodlines? Arcanum? I'd put it comfortably above other relatively recent high quality RPGs like Pillars of Eternity and Fallout New Vegas, which I also enjoyed but didn't resonate on a deep level. The writing with respect to the individual characters and the setting are top-notch, even if the central story lacks in some respects, and earns the game a place in my pantheon of great videogame storytelling experiences.
How do I think it compares to Planescape Torment? Having replayed that game recently: quite well! PST is a more coherent game, from a storytelling perspective, and that gives a good argument that it is better from a literary view, but I didn't think the setting was as fascinatingly varied and exotic, and the quests aside from the central storyline weren't as consistently engaging. Combat in PST was also, rather than being deeply flawed, fundamentally bad and odious. Character wise, PST has an edge, because each companion related thematically to the central storyline, though I found that the common thread of the binding nature of torment and suffering was a little relentlessly dour.
On the whole, I'd say they're closely comparable in the level of enjoyment I derived from them. I suspect my view that they are comparable in terms of overall merit is premised on my affinity for Dying earth science fantasy settings over straight fantasy settings, even ones as strange as Planescape, so take that for what its worth.