I found it boring and another exercise in loose continuity*.
*First the black oil’s presented as a sapient intelligence that takes possession of human hosts, then it’s a virus that sends people into catatonia, then it’s alien semen. I guess its effects are whatever the hell Carter wants them to be at any given moment.
Bolded that last bit since it’s the most accurate description of The X-Files as a whole I’ve ever seen.
For the record, I think season 8 was the best season of X-Files after Fight the Future. It was a great return to form after the “meh” season 6 and the mostly-abysmal season 7. They should have ended it with 8 and either not introduced the super soldier stuff, or kept 8 as it aired, took a few years off, and done a movie or two to wrap up the super soldier plotline.
Season 9 was hot garbage all the way through, I Want to Believe was aggressively average and handwaved the series finale away in terrible fashion, and the only thing worthwhile about season 10 was the Were-Monster episode.
For a while I pretended the show ended with Mulder’s abduction in the season 7 finale and disregarded season 8 onward because I remembered hating it when it aired, but I rewatched everything in the lead up to season 10, and season 8 turned out to actually be pretty damned good. So as it stands now, season 8 is the ending for me unless season 11 turns out to be absolutely goddamn amazing.