I haven't heard everything they've done in the early days, but what I have was really hit and miss. Their debut was kind of shitty imo, I know they remade it with different drums and changed a bunch of stuff, but I don't know if that version is better or not. Sky Moves Sideways was alright, but way too derivative even for them. Voyage 34 is a pretty cool psychedelic epic though.
Signify is when they actually get pretty good crossing their very obvious influences with some good songwriting and psychedelics that sound, if not very original, at least genuinely like themselves. After that they were pretty consistantly solid.
In Absentia is a genuinely great album. that album was to me in middle school what OK Computer was for a lot of people (theyre both modern art rock albums with impeccible production, a heavy pink floyd and classic rock influence, and they're proggy but not too proggy, complex but not inaccesible, theres both heavy tracks and lush ballads, ect).
They lost me a little as they became more and more metal influenced though I liked Fear Of A Blank Planet a lot in spite of that (a lot of their fans consider Deadwing to be their best album, though it was never a highlight for me). Their final album The Incident was a total miss and saw them turning into the dream theater wannabies that they had avoided being up until that point (though it's still far far better than dream theater).
Steven Wilson's been spending the last decade buying into his own hype and fashioning himself as some savior of modern prog and making some of the most thoroughly mediocre prog ever because of it. He also wastes a lot of time remixing classic albums that don't need to be remixed, and ruining Opeth by turning them into prog act only slightly more mediocre than himself. I'm hoping he'll bring Porcupine Tree back and return to form one of these days though.