I agree with his points about the game screen being hard to see (with the fog of war) and inventory management from today's perspective. U6 is one Ultima I don't revisit pretty much because of those two things.
However, failing to put some context to those game designs is disingenous.
HARD TO SEE
U6's graphics were cutting edge for an RPG in 1990 when the game was released. And while the scope of what you see at any one time given the size of the window from which you see all the action, it looked quite sizeable on-screen as typical resolutions of the time were 640x480 and 800x600. I think the fog of war issue isn't nearly as bad if you play U6 with a much lower resolution (as strange as that sounds).
INVENTORY MANAGEMENT
Inventory Management also needs some context as the video review really complains about all the items that need individual managing. Today's developers are all about streamlining - one of the biggest complaints by many people here at this site when it comes to RPGs. But back in the 80s and early 90s, Richard Garriot's approach was quite the opposite. In one of the books I have about the Ultima series, Richard brags how every single key on the keyboard has a purpose when playing Ultima 4. And back in those days, I couldn't be happier about that. Computer games back then were supposed to be complicated, with arcane, undocumented features and functions. It was a great departure from the simplistic offerings of videogame consoles of the time. So when it comes to inventory management, that was actually sort of fun, at least for me, back then. All those in-game objects that could each be manipulated separately, it really was a novelty. By today's standards, that is arguably not the best approach for inventory management, but back then, players like myself really liked that sort of thing.
MY TAKE
When I played and completed U6 back in 1990, it was the one and only time through U6… which joined the rest of my one-time-through family U8 and U9. The rest of the Ultimas I've played multiple times through. About a year ago I tried to play U6 and just didn't like the small game-world window and the 'fog of war' effect based on lighting and line of sight. However, I do remember really enjoying U6 when I did play it in 1990… I do have positive memories of that play-through and remember looking forward to playing that game every chance I had until I finished it.