The short version, for those who did not play CK2 for copious hours or are new to the series, is that Crusader Kings 3 (CK3) is a good game. Imagine the Sims crossed with a medieval strategy board game. You plot, fight, and pray your way through history as you seek to ensure the survival of your dynasty. If you have a passing interest in history, RPGs, or strategy games you will probably enjoy it.
I would like to address the rest of my review to those who have a history with this franchise. It is hard to compare this game to its predecessor. However, that is obviously the question on everyone's mind and we must fairly compare the two without years of nostalgia. I will try to do so in a concise way that does not go too deeply into the weeds.
CK3 undoubtedly has more content then the base game of CK2. On a one-to-one basis, it's not a fair fight. The religious system has been vastly improved. Whomever paradox hired to research the various heresies, sects, and doctrinal differences of the medieval ages did a fantastic job. While the ability to create your own sect might seem far fetched, and at times it is, but its not too over the top in my opinion. If you don't want to abuse that system, you don't have to. The map and to a certain extent the UI is also improved. Though it does take some getting used to.
There are some stylistic choices, such as the new portraits for the characters, which I feel are subject to personal preference. Some will like them more than the old ones and others will not. I did not find such stylistic choices to be a game-breaking experience.
The big problem obviously looms when you compare CK3 with the CK2 of today. The CK2 with years of DLC to flush out the game. In that respect, CK3 is found wanting. The first country I played as was the Eastern Roman or Byzantine Empire and immediately I noticed a lack of content. While CK2, even with the Heir of Rome expansion, never really managed to do true justice to the Theme System, they didn't really try in CK3. The ERE is a feudal monarchy in the same mold as France or England. Strangely, they kept the option to mend the Great Schism and reforge the Roman Empire but gutted everything else. Also, trade routes have been completely removed from the game, another cut from the CK2 compendium. These and other glaring omissions scream future DLC content and I have very little reason to doubt I am wrong.
So does base CK3 live up to its family legacy or is it the bastard child of Imperator? Honestly, it's an above average son who will not go down as particularly great or terrible. It's good, generally polished, and if you play as a France there is a good chance you notice more good than bad. However, it suffers from the effect that many new paradox games have suffered from and that is a policy of digging a semi-functional well halfway down, selling it, and then coming back later to finish the job. It's playable, its fun, but you can't help but notice what is missing or where they could have expanded the improved mechanics but didn't. But don't worry, in a few months the game will be fleshed out with DLC and surely they will treat us better next time.