The notion of Vader having very little variety tends to make less sense the more you listen to their albums. Sure, the band doesn't stray TOO far from their foundation, but there's always a different element emphasized depending on what release you're listening to. Though you can trace the progression throughout their discography, in reality The Beast sounds nothing like The Ultimate Incantation, it's even pretty far removed from Litany, and it doesn't sound much like what the band would evolve into by The Empire. Also, this variety between albums is the only possible explanation for why Vader could release an excellent album in Revelations and then follow it up with something like The Beast that seems alright from the outset, but hasn't really stood out in any way by the time it's over. It just sort of...happens, and once it's done I have this faint memory of listening to a Vader album, but I can't even pick out a riff I particularly liked.
So what's different about The Beast, then? Mostly the melody. Vader discovered their signature sound on De Profundis, and then spent a bit of time slowly fattening it up until Revelations. After that album, they must have realized that they wouldn't be able to do anything as heavy and punishing as Litany despite their best efforts, so on The Beast you can see them opting for a slightly more melodic direction that they would mess around with for a couple of years. I don't think they've ever written anything as light and accessible as "The Sea Came in At Last". That song and a couple others feature some delicate, non-distorted guitar lines. I never thought I would hear those on a Vader album until I heard The Beast. The faster riffs are less straightforward and blunt, with little extra harmonies and flourishes that were there in trace amounts on Revelations now becoming the focal point. There's more solos on this as well, and they're more simplistic and sustained, less chaotic and Azagthothy, also indicative of The Beast's more melodic direction. There also seem to be more chuggy, groovy moments...or at least they feel like they're going on for a lot longer than they usually do. Vader are usually at their best when they opt for short, punchy songs, and all of the tracks on The Beast clock in at around three and a half to four minutes. That doesn't seem like it's very long, but given the fact that this doesn't quite have the same immediate punch that their previous albums did, these songs tend to feel a lot longer.
Part of that might also have to do with the drumming. Doc was supposed to be the dude layin' down the beats for this one, but apparently he broke his hand so the drums had to be recorded by Daray, who ended up staying with the band for a few albums. If my logic is correct, that would mean that Doc created all the drum patterns during the writing process, and Daray just played them as closely as he could to the best of his ability. Not that it's necessarily Daray's fault, but his presence on the album may contribute a lot to why The Beast isn't as engaging as other Vader albums despite the groundwork being the same. He just lacks those little extra accents that Doc used, especially during the slower sections, and as a result the grooves just aren't as groovy. On The Beast, he just sound like he's trying to follow Doc a little bit too closely, which makes sense given the circumstances, but he doesn't have that x-factor that pushes the songs to the next level. Fortunately, he would come into his own in a big way on Impressions in Blood, where he sounds more comfortable and like he's doing his own thing.
Even though the more melodic sound on The Beast isn't necessarily a positive, I wouldn't say it's the sole reason why this is one of Vader's weaker albums, either. Piotr doesn't really sound like he's trying as hard with his vocal lines (and the clear but thin vocal production doesn't help matters much in that regard), and generally the band doesn't really sound as inspired as they usually do. When you take out the clean guitar parts and the extended solo sections, there aren't a lot of interesting songwriting quirks to draw your attention one way or another. I wouldn't go as far as to call this a bad album, though. If you'd never heard a Vader album before, this would probably sound fine. Unfortunately, they have an extensive and varied discography, and pretty much every trick you hear on The Beast has been done better on another album. I'd rather listen to this than The Ultimate Incantation, but given that album's position as an idiosyncratic debut, The Beast may very well be the most disposable Vader album. Who knows what their later work holds, though...