It's old, but it's aged well. This fic created a lot of the fandom's most popular tropes, because it used them so well that everyone else wanted to do the same thing. It started as a short story (hence the sudden twist a few chapters in - that was a dare in the General Worm thread!) but it beautifully managed the transition into a multi-fic series with incredible plot, fantastic characterization and the good aspects of the tone of the Worm serial.
Most Worm fanfics break off from canon in some way or another. Some give Taylor, or other characters, new powers. Many give them new personalities, intentionally or not. A few try to lighten up the normally-grim setting with some slice-of-life fluff, while others dispense with the darkness entirely and crank up the humor. Only a small number of Worm fanfics really attempt to emulate Worm itself, preserving as much of the original's style tone as possible while taking things in a new direction. Of those, fewer succeed. And of the ones that do, Cenotaph is the cream of the crop. There's a long list of Worm fics that I would call classics, but if I had to condense it down to a single story, it would be Cenotaph. First and foremost, it does a remarkably good job at preserving Worm's signature "everything gets worse" feel while combining it with the constant escalation that Taylor is famous for. Much like in canon, capefights revolve around careful strategy and clever power usage, the stakes are constantly raised through a combination of cape politics and violence, and victories are rarely as clear-cut as they seem. Furthermore, everybody is in character, especially Taylor (which is a rarity); all factions are intelligent and pursuing their own goals; and suspension-of-disbelief-straining events are few and far between. One of the other noteworthy features of Cenotaph is the worldbuilding. The author, notes, spends a considerable amount of time fleshing out canon characters that never got much attention via interludes, and in a manner entirely consistent with the characters' known traits. notes also introduced several setting elements, such as Coil's company Fortress Construction and Lung's affinity for La-Z Boy armchairs, that went on to become some of the most persistent pieces of fanon. Fans today are still often surprised to learn that Fortress Construction isn't actually canon. That should give you a good idea of Cenotaph's influence. If Cenotaph has a flaw, it's that things progress a little *too* quickly. Worm spread out Taylor's actions up to the Leviathian fight across nearly eighty chapters; Cenotaph does it in under forty. Coil goes down within a couple of chapters and a bit anticlimactically. Taylor also grows accustomed to her powers significantly faster than in canon without good justification, such as learning how to hear and speak through her bugs within days instead of several weeks. Everything she does is still believable, but it doesn't create quite the same level of excitement as canon Taylor constantly inventing new tricks and tactics on the fly. (Pun intended.) There's also a couple of somewhat forced coincidences during the series (spoilers!), such as Bakuda uncovering Taylor's civilian identity through sheer luck, and a bigger coincidence in Wake that I won't describe here--those broke my immersion when they happened. Lastly, Taylor gets plenty of characterization throughout the story, but there's a bit less of an emphasis on her interacting with other characters due to her becoming a solo hero. That limits the options to an extent. That being said: Cenotaph is still, in my opinion, *the* classic Worm fanfic. It's not the most escalation-heavy (Weaver Nine), or the one with the best character interactions (Mixed Feelings), or the funniest (THE TECHNO QUEEN). Yet it and its sequels are quintessentially *Worm* in a way that hardly any other stories are. tl;dr: If you've read Worm and your response was "I want more of this," then Cenotaph should be the next thing on your reading list.