These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: The members of the Fellowship at the end of the game. They essentially low AI controlled character classes and are a LOT weaker than many of the enemies you have already killed to get to them.
In the northwest forest of Britannia, there's a house full of goodies whose door can only be opened by a lever on the inside. Normally, you need to go through a dungeon and find the teleporter that will warp you into to the house. However, if you position yourself by the window so that you can see the lever, you can just use Telekinesis to open the door (in Exult, you can simply change the screen resolution if you can't see it right away).
Sometimes a glitch will allow you to enter the Sphere Generator without the Enchanted Hourglass.
Visit A Fistful of Ultima VII for a detailed list of Good Bad Bugs and a hilarious anti-walkthrough which exploits them to win the game in completely unintended ways.
Using serpent venom causes temporarily ups all of your stats, but after it wears off, it degrades your strength slightly. If you use enough of it all at once, though, dropping your strength rolls over and leaves you with an absurdly high stat e.g. 164 or 135 when the normal max is 30.
It's possible to apply potions and certain items to non-party members, meaning you can poison NPCs without backlash or temporarily put a dragon to sleep without casting a spell.
Porting Disaster: In the SNES port, the plot was mostly the same, but wound up being butchered as a result of Nintendo's Never Say "Die" policies at the time. The double homicide that starts the plot of the game is replaced with a double kidnapping...that never gets solved! The entire combat system and party system that defined the original game is dispensed with altogether in favor of a Zelda-style action RPG format in which the Avatar wanders around alone whacking snakes and bats with his sword.
Scrappy Mechanic: Having to manually feed your characters. The fact that they can't feed themselves is made fun of in various fanfics, with the Avatar giving his companions nappies and spooning food in their mouths.
Kill the mother of Lord British's unborn child, and there's a baby in her inventory. Ick.
The game allows you to make bread with buckets of blood.
Technology Marches On: The game had a notable bug in the release version which dealt with the Lich in Skara Brae. To have it fixed you had to contact Origin, who would send you the patch... on a diskette, via snail mail. This was right before everyone started getting the Internet, so it was one of the last examples of this.