It is infested with something called scale. It looks like a severe case of it, too. In the early stages, you can deal with scale by removing the individual infected leaves and treating the plant with one of a wide array of pesticides.

There might be applicable heroics in your case but I doubt it. You may have to restart it from an uninfected cutting.

You will also have to get rid of that plant, unfortunately. When you do, you will have to dig it all out, put it in a bag and ask around your locale how to dispose of infested plants. Do NOT put it in your compost. Moreover, you may have to fallow the spot it was growing on, inspect the other plants around it and deal with those infestations as well.

Yes, scale infestation this advanced is that serious, I'm afraid.

Yeah, scale's not fun. It also spreads, so keep this away from any other plant.

If you can get an uninfected cutting, take a daughter. But isolate that as well until you're certain it's really uninfected.

One thing you might try (try) is to spray the entire plant thoroughly with neem or wipe leaf surfaces with rubbing alcohol to try to kill the scale. I'd go with the neem first, and then wipe down leaves later once you see what remains later.

As always, mind neem a little bit: http://npic.orst.edu/factsheets/neemgen.html

It's killed cats and caused problems in rat studies with pregnant rats, so...

During the process, keep the plant fully isolated from other plants and wash your hands thoroughly after working with it (and not just because of the neem oil).

With a plant that nice, I'd try to save it.

Worst-case, cut the plant back to far fewer leaves and work on those, allowing the plant to re-sprout leaves as it can in spring and recover that way.

Do the spots rub off or scrape off easily? It doesn't look like scale to me (which would also be present on stems as well) and if the spots cannot be easily removed, then it's very likely oedema, something that many fleshy leaved succulents can be prone to if exposed to excess water. When subjected to steady rainfall for a period of time, the roots just absorb more water than the leaves can release back to the environment and spotting or pitting and sometimes even corking results.

If the oedema, the plant is not dying, it is not a disease nor an insect and needs no treatment other than to protect the plant from excess rainfall. Unfortunately, the appearance of the damaged leaves will not change so you will need to just endure the spotting until they fall off naturally and are replaced with new :-)

See my similar comment your duplicate thread.