I bought this Spanish original because I wanted to know what I was missing in the English translation. The answer is not much, because the English translation is pretty good.
In early 2007, I bought and read the English-language translation, Reminiscences of the Cuban Revolutionary War: Authorized Edition (Che Guevara Publishing Project). (I have reviewed that translation on Amazon in very positive terms.)
There are very few surprises when I compare this Spanish-language original with the English translation. Turning over the pages of both versions, it's difficult to see any difference at all (apart from the language!). However, the differences do make it worthwhile to obtain and read this Spanish-language original.
* The "editorial note" ("nota editorial") is different in the two versions. In particular, the Spanish version says that the corrections to the 1963 edition have been highlighted in bold-type, whereas the corrections are included in the English translation without highlighting.
* The English translation has an additional two and a half page "biographical note on Ernesto Che Guevara" (pages XI-XIII).
* The English translation makes numerous small deviations from the original. For example, the original "A pesar de nuestro aspecto patibulario..." (page 16) is translated as "We must have looked like a bunch or pirates...". On every page, there are a few omissions, additions and modifications. As another example, "...cercerían la casa de guano por la extrema derecha" is translated as "...[they] were to surround the palm-thatched quarters on the right side". It is very certainly not a bad translation, but it could have been more precise!
* The English translation usefully fills in the full names of people in square brackets, whereas you have to guess many full names in the Spanish.
* The English translation also usefully adds year numbers in square brackets, and adds the months where the original gives only the day of the month.
* The "Glosario" in the Spanish original is missing many of the mini-biographies which are in the English version.
* The binding of the Spanish version seems a bit weak compared to the English, and the Spanish-version paper is heavy and bright white.
You get almost the same thing in the English and Spanish language versions. The English version has many useful little pieces of extra information, but the English translation has some imperfections. So I think it's best to get both of them.
As I have mentioned in my longer Amazon review of the English-language version, I think that this is one of the most compelling first-person historical accounts I have ever read. It is full of humour, humility and horror. For the rest of my comments, see my review of the English translation.