Having played the DLC for a few evenings, it's about on par with the base Talos 2. Competent and entertaining, but not transcendent. The first part Something Something Orpheus focuses on the laser connectors and introduces a new twist that hasn't been used anywhere this far but unfortunately doesn't do much of note otherwise. The bonus puzzles on the other hand are devious and inventive enough that I haven't been able to crack any of them.
The second part Isle of the Blessed features the insufferably effete green robot in the middle of a Dawson's Creek episode solving a nice variety of semi-difficult mixed puzzles that use the other tools from the base game too.
The third part Into the Abyss is the true successor to Gehenna. The puzzles are elegant yet fiendishly hard. The setting takes a Psychonauts-style turn inside a mind broken by grief, doubt and regret, and even Elohim returns to offer some guidance. I'd like to say more but the difficulty spike is so harsh that it will take time to make any progress.
Playing (but not finishing) the DLC in sequential order, I was slightly underwhelmed by the offering before firing out the 3rd part where the puzzles and the setting start to come together. The first part is nice, but short. The second is nice too, but more of just a continuation of the 7th/8th puzzles from the base game worlds, and some annoyances from Talos 1 puzzles also resurface here. Talos 2 was admirably free of ambiguous puzzle setups unlike its predecessor where some solutions required you to almost accidentally discover that oh, it's possible to jump over that fence or that oh, the machine guns won't shoot me if I ride past them a bit higher up. Isle of the Blessed has a few of those: oh, I can put that object through that hole but not that other object.
The melodramatic plot in both where robots as detached observers dig deeper into the human condition and try to reason love from first principles has potential, but crumbles under a severe misunderstanding of conflict as a cornerstone of all life, some annoying redditisms, and too much focus on unremarkable side characters from Talos Principle 2. I have no recollection what "Sarabhai" or most of the other robots were doing in the base game whatsoever, it's like trying to continue reading Hundred Years' Solitude after a 6 month break. There's also some Anomaly and wormhole travel has become ordinary and I don't know what else. Maybe I got the wrong ending in Talos 2?
Everything is redeemed in the final act though. It's just Byron and Athena, two core characters from the story. The puzzles as stated are excellent - even if you dislike the difficulty, their elegance is admirable. The setting creates a dramatic tension that's not present in the rest of the DLCs. About the only gripe I have is that the voice actor for Athena isn't on par with the others but it's more than offset by the return of Elohim.
Overall, there are probably about 70 fresh puzzles here. Into the Abyss itself has as much content as Gehenna, and that's less than half of the total package here. Unless you unambiguously disliked Talos 2, no reason to skip this.