TL;DR first: If you are a newcomer to the Dark Eye looking for more information on Aventuria, or you're a GM looking for a late-medieval fantasy world with a very traditional elves-orcs-dwarves-and-knights feel to it and appreciate the minutia and little tidbits worked out for you that makes a world feel "lived in" while preferring to come up with the 'exciting' stuff yourself, buy this book.
Now, as a long-time fan and player of the german Dark Eye, I of course run into some issues here and there that pop up due to having a strong opinion on some aspects of the lore and this and that, but none of these are good reasons to deter a new customer:
If you are interested in playing/GMing The Dark Eye 5th Edition, this is an essential product, and to date it is probably the best world-almanac this game world has seen in how it balances depth of information and presentation. You get a good, panoramic view of Aventuria with enough to boost your imagination in visualizing the setting, without being overwhelmed.
Every article on the geographical regions is accompanied by a landscape illustration that for the most part manage quite well to convey a good impression of that corner of the world (and I wished the same was true for the chapter on important cities, alas, this one only has the crest of each location). This is where a lot of the meat of the book is, and I found most information contained herein to be very solid and sufficient to cook up some adventure and campaign ideas. A highly valuable part in Chapter 3 on Locations and Settings is the real-world inspiration named for each country, so you can extrapolate additional information by doing some real-world research if you feel like fleshing out a region without waiting for the indepth sourcebook that will eventually (but probably years in the future, even more so for the english translation) be released on that topic. As for the cities, they perhaps fall a bit flat for a GM trying to use this information to run a city-based campaign there, as you get only the roughest impression - but if you are looking for stuff to play a character from any of these cities, you will find plenty to go on.
As for the rest, you will find chapters on science, language, records of time and history, a brief look into cosmology, the dominant faith of the world, information on the aventurian feudal system, military jargon, a bit on what people eat and what sports they play, commerce, law, and all that kind of neat stuff that will help you create an immersive experience, which is the section where the Dark Eye itself and this book excell. If you don't care for any of that stuff, then you will find no use for a good 50 page chunk of this product.
A specific gripe I have personally with this book is Chapter 6 with the Aventurian Bestiary, where some very ubiquitous creatures such as goblins, ogres, orcs, trolls, some multi-legged creepy-crawlies, the stanky quasi-dragon Tatzelwurm, wolf, boar and bear are described and given stats. Now, that in itself isn't so bad. It may feel anecdotal to be in here, but I do see the point in how these very 'universal' beings have a bit of a place in the universal setting book - the part that grates my cheese is that these creatures are NOT repeated/integrated into the Aventuria Bestiary book sold separatly (which also does NOT contain the handful of creatures contained in the Core Rules book). I despise this sort of fragmentation that, as a GM, makes me miserable when I have to juggle multiple manuals to find what I want.
(Tangent: Some people say that is adressed by the official rules-wiki but so far that only goes for the german version - so far I am not aware of an existing english rules-wiki - , and even then I find it to be a bit of a consolation-prize-solution at best.)
Another low-point of the book in my opinion is the very short chapter on races, where humans, elves, dwarves, orcs and goblins each get about 3/4th of a page of text, that hardly contains more information that you have not already gotten in the core rules - in arguably MORE depth when you read the entries for the respective cultural backgrounds.
That said, if you do not intend to run this world with the Dark Eye rules and rulebook, I suppose this makes the Almanac a more 'independent product', so your mileage may vary. Following that thought, the book has little to no rules that are system-specific, so if you are the type who likes to have setting books be system-neutral, this is for you too.
While I am tempted to only give a 4/5 for the gripes and warts mentioned above, my gut tells me that this is a product I would still "highly recommend" to anyone interested, so if you take the rating as a recommendation to buy the product, it gets a 5/5, and this is what I'll do. If you consider ratings to be more of a "critical score" for the sake of just rating the product in itself, then it's "very good with some minor drawbacks", so there you go.
[5 of 5 Stars!]