In my opinion, this is one of the most solid experiences ever when it comes to extreme demons.
Unlike with many other extremes out there, where you find yourself measuring your progress on the level by how many chokepoints you were able to get through, Heartbeat is, in my opinion and basing myself on my own experience with the level, more or less a fair experience.

The way the difficulty goes is as follows: the first 50% is hard, mainly because you have to learn it and master it, but once that's done, you'll very rarely die to it.

The wave part is probably not as hard as it seems, but since its fast-paced, you're probably nervous, and some parts are quite awkward gameplay-wise, so it is very likely that you'll die to it a lot.

The remaining 30% is a bit all over the place. After the wave part. you're immediately thrown into a fast ship part with precise clicks, which is already hard on its own, but we also need to consider the fact that you have to successfully go from spam gameplay to precise inputs, making it even harder. The robot part I can only describe as "tricky". The gameplay is deceivably simple, which might have you underestimate the real difficulty of this part, making it therefore quite chokable. The imputs on that part are also strangely tight, I personally ended up beating the level despite not having a consistent way of making it through that part. And finally, the end cube is really easy, though I do recall it being harder in 2.0, so I'm guessing the new physics made it free.

Looking back at it, I'd say it's pretty balanced when it comes to difficulty, and it is not chokepoint-heavy at all (the only annoying part being probably 8%), despite my personal experience telling me that there is a "hardest part", that being the wave and the ship immediately after. But I do realise that the only reason that's the case is because of nerves, making that part of the level a way tougher experience than its actual difficulty might suggest.
And here's the thing: that's the intended experience. Or at least the progression on the song and the decoration seem to point towards that being the case. In a way, since the level goes from being chill, to being nerve-wracking, back to being chill once again, I'd say beating the level feels "swift" (that's the only word I could think of to describe this feeling).

Decoration-wise, it's pretty standard for the time. What makes it stand out is just how immersive it feels despite being this simple. I won't say it's the most immersive experience out there, but compare that with how simple its decoration is, and you might understand why I find it to be so noteworthy.

It is also important to make it clear that this level did not push any limits for its time, so the highest I'm willing to rate its decoration is an 8/10.

All in all, if you're into themed levels with a uniform kind of gameplay all throughout, and it's within you skill level, chances are you're going to enjoy this one.