This is more in the range of a novella than a novel.
This is a speculation about what the far future might be like, written in 1890. There are many references to science and scientific terms (of that era) used in the book, which perhaps qualifies it as "science fiction". However, some of the science is archaic, some may have been plausible speculation at the time but is unconvincing today, and there is some mumbo-jumbo (such as references to the supposed feats of a 19th century Indian guru).
Prospective readers should also be aware this is not a “story” in the sense of plot or character development. This is something more like a tour of a few points of interest in the future, with some dialog between the tour guide and the tourist.
The language is stilted / stiff, at least by modern standards. It would not have been as out of place in the Victorian Era. And the author tends to use sentences full of longer words, to the extent that other Victorian writers did not necessary do. Characters speak to others (or think to themselves) in long-winded passages in a manner that might remind you of people who like to hear themselves tell everyone else how much they know.
One aspect that struck me was the depiction of future humans as having huge heads / brains and petite limbs and hands. Such future humans have appeared in a number of (mostly classic) SF stories. I was curious whether this might have been the first instance. However, I don't have an answer to that.
It's worth noting that in this future, the advanced humans are a mix of African and Oriental ethnic backgrounds. Caucasians are essentially a thing of the past. The future humans view Caucasians as having been too war-like and not having contributed much memorable to humanity. By 19th century standards, a relatively positive view of Africans is presented. However, the description of the African-Oriental mix attributes the positive mental characteristics of the new race to the Orientals. So, comparing it by modern standards will give a less positive reaction.
While I tend to be pickier than most people about the plausibility of supposed science in SF, I am more forgiving if there is no suggestion of mumbo-jumbo and there is no "explanation" of the questionable element (which draws more attention to it). The premise of the book is that a member of an 1896 expedition to the North Pole is frozen in ice and thawed out 10,000 years later. No reconstructive surgery, prosthetics, skin grafts or similar treatment seems necessary. There is a long discussion about 18th and 19th century experiments on thawing frogs and other cold-blooded animals from earlier in evolutionary development. The explanation is made even longer by telling of doubtful suspended animation achieved by the Indian guru. Perhaps, this didn't seem so far fetched 120 years ago, but today I would have rather that the author merely say a man was frozen and thawed - then get on to the story / speculations about the future.
The future humans can levitate and travel from place to place at any speed they want by a mental power. It is explained that their minds generate a "nervous atmosphere" around them that makes this possible. To add insult to injury, they apparently can do this essentially regardless of the weight of objects they carry, distance or time without tiring. This power seems to be associated with their extra-large brains rather than being attributed to a supernatural source. So why would Boussenard - a physician - think these would not constitute exertions that would have certain limits and cause a person to tire?
It seems surprising to me that something written in 1890 does not anticipate a future with more machines, industry or other sorts of technology. Most of what is new is uses of the mind. One (partial) exception to that rule is communications with the inhabitants of Mars. This is done by using a vast number of cloth sheets to change the color of a substantial area of land on Earth so the change in color can be seen by Martian astronomers. It may make a certain amount of sense given the technology of 1890, but unfortunately it has since been made to look odd considering today we would try to use radio. The first tests of radio transmissions were not carried out until later in the 1890's. It is also curious that this story was written 25 years after Jules Verne's From The Earth To The Moon, and yet 10,000 years later humans who can fly anywhere on Earth instantaneously have not yet found any way to visit Mars.
As one might tell from this review, I was not impressed with the story. However, if 19th century views appeal more to you, or if this review has piqued your interest, give it a try.