@JonnieCache covers a lot of points about the oscillators. It's not just that Serum offers a wavetable lookup oscillator, but one that can scan through a wavetable in realtime, "Warp" the sound in various way (including FM, PWM, hard sync, stretching) without aliasing. Then there's also the tools to draw, mathematically generate or import your own wave files, and make wavetables blending between them (from simple crossfading to FFT blending, etc)

There's a ton of filters, I'm sure you could find the basic LP/BP/HP filters, but I know some of the moog-style filters have to be licensed. There's also filter options that aren't typically considered "filters" (flange, allpass with multiple stages, a weird reverb-esque one), and a few filters that are just Duda's own experiments (I think he said the French LP model was just him playing around with the math).

Then you'd also have to reimplement the FX section, which Serum also provides as a standalone plugin that you can place after other audio sources.

Still though, the GUI is a huge benefit of Serum, which makes editing waveforms, envelope curves, LFO shapes, and modulation routing really easy. Almost anything can be routed to almost anything else, as well as several macro controls, which makes it a great live instrument too.