So, I'm coming at this as someone who read the whole series way after it was popular, and honestly? Volume 1 feels like a very specific taste. It's got that super early-2000s shojo aesthetic, which I have a weird nostalgia for, but the pacing is glacial. You spend a lot of time in the moonlit academy setting, and the main love triangle between Yuki, Kaname, and Zero is introduced with this intense, brooding atmosphere that can feel a bit over-the-top now.
I think whether it's 'worth it' depends on what you're looking for. If you want a fast-paced vampire action story, you'll probably be bored. But if you're into that particular brand of dramatic, gothic romance with a lot of lingering stares and tragic backstories hinted at, it's kind of a classic of the genre. The art is gorgeous, though, and Matsuri Hino's detailed costumes and settings are a big part of the appeal. I kept reading mostly for the art and to see where the wild plot eventually went, but the first volume alone is a bit of a slow appetizer.