Civilization games are properly reviewed after putting hundreds of hours in, not a merely a few dozen that obviously some of the reviewers, and even critic reviews are obviously not played enough to see the glaring issues that Civ 6 has, don't get me wrong here in the fact I do like Civilization 6 its just >right now< its not nearly as good as Civilization 5, but with time and alot of balancing and fixes it could be just as good, I doubt it'll be better, but it can be just as good imho, and that comes from a hardcore Civer since Civ 1.
The problems with Civilization 6 are numerous, from limited options - to bland and highly predictable A.I and unfortunately, the god awful cheating scripts are back on higher difficulties to fake increased difficulty. So, lets start - Barbarians need better options, currently its off or 'rampage mode' since they all have a high spawn rate, they need a more options. Next up is the slow paced gameplay, standard modes pacing is very odd, at times it feels like a Marathon game then quickly speeds up then slows down..the pacing feels all over the place, and because of that - the A.I which tends to follow the date is terms of advancement can suffer too, a classic example of this would be;
Player increases research and lets say enters industrial period, the date per turn will usually increase/decrease depending on the date, lets say its 1500AD, the DpT will increase for a while until its more in-line with the era, for some reason that seems to give the A.I huge buffs and they'll rapidly increase in research and power sometimes, heck - I've seen them jump from renaissance period to modern period extremely fast defying all logic, but since I've seen England get Ironclads as early as the 1200AD...honestly it doesn't surprise me since the pacing is definitely way off the mark.
A.I is stupid, obvious and stupidly good, the latter is the problem because it will attack with better strategies than the previous games, however the major problems is that alot of the times its rather obvious what its trying to do - such as Sumeria spawning 20 war wagons and then slowly moving them to your civilization to launch a surprise attack...well *I'm* surprised the A.I did that - wow! Another problem is the fact the AI hates human players, to a point there isn't any reason to be nice to them, they'll break every single promise you make with them, they'll attack you relentlessly and the diplomacy is plain weird to a point it just feels broken, don't get me started on how broken the warmonger system is - essentially by late game the world threatre is pretty much everyone hates everyone and denouncing is just rife.
Another major problem is the fact that the game feels so slow paced compared to previous games, districts take way to long to build, especially late in game where its not uncommon for it to take 30+ turns for one district, because of the pacing issues, making spawling and large civilizations is nearly impossible to do now. I could go on and on here about all the issues, from nitpicking about special ability balance such as Electronics Factory, or how the game suffers from strange bugs that cause input lag, especially late game so I'll just close with this statement again;
Civilization 6 right now, is no way near as good as Civilization 5 at this present time. With patches and some expansion packs it could be great - but Firaxis needs to fix alot of the mechanics and do some balancing.