It was a great album. Is it the best....nah! When I first heard of Tristania back in 1998, I though Widow's Weeds would be their best of all time and I still think that today. Beyond the veil defintely had better production quality but it wasn't as dark as the previous.
Maybe you like WW more, which is your opinion. Darker doesn't mean better. Instead, it is only fair to say which
album you like better.
Generally I don't like comparing Tristania's albums, because they all move me in different ways. BTV isn't as dark as WW in terms of atmosphere, but it doesn't need to. (btw, the term "dark" is quite subjective, there are people who think BTV is darker) Just as their other albums, BTV simply describes an entire different emotion. While WW conveys sadness and cold, BTV is deadly and elegant at the same time. The vocal arangements on BTV are unpredictable and more extreme (both operatic and growling vocals), at times they sound like a battle between heaven and hell, the music is also more complex and faster pace than WW. As much as I love WW, I personally think BTV is deeper and better composed in terms of lyrics, structures and arrangements.
In conclusion: You have to hear it for yourself to decide which one you like best..