I have noticed that the various version of Ultima 3 seem to differ in rather subtle ways; this topic is here to list those I am aware of. Specifically:

Apple 2: Haven't played this version, but it appears that you start with only 100 HP (instead of 150 HP), so your HP is 50 less than in other versions. (Maybe the developers decided the start was too unforgiving after this version was released?)

DOS: The overworld encounter rate is *really* low in this version.

Amiga: I noticed a few differences here:
* Rangers regain MP quickly in a manner similar to Druids, but with the roles of INT and WIS swapped. (This makes Rangers probably the best class in the game, and it obsoletes Druids in this version.)
* Accuracy is affected by position in the party; the first character doesn't need 99 DEX to hit reliably, while the fourth character can't hit reliably even with 99 DEX.
* The RNG is less random than it should be, and seems to have a lot of streaks. For example, if Appar Unem fails, if you keep trying it, you will likely get a lot of failures before it succeeds. Mass attack spells (which have a 75% chance per enemy to hit, I believe) frequently hit all enemies, and I have seen such spells hit nothing far more often than would be expected if the RNG were perfect.

NES: This version differs substantially from computer versions. I won't go into all the details here, but:
* Druids do not get fast MP regen, making that class considerably less useful.

MSX Cartridge version: Based off the NES version, so the changes there also apply, but I have noticed one other thing:
* In (at least) Castle Britannia, MP recovers at a rate of 1 every 2 steps (not 1 every 4, as in the NES version and the computer versions I've tried).

Anyone know of other little differences like these?

Also, anyone have any Ultima 3 versions to recommend? (I've played DOS and Amiga, and decades ago I played NES (and am thinking of giving that version another go), but are there any other interesting versions worth looking into?)

Hmm, I've only played the C-64 version of U3 because it was superior to the other platforms until upgrade patches happened. I've seen it played on an Apple IIe way back when, which is what introduced me to the games.

I don't recall the issues you mention though admittedly I didn't spend much time observing mechanics. All I recall is everything seemed to work right such that I didn't have any complaints.

- Overland encounters happened frequently enough to keep me from thinking the world was unpopulated.
- Dungeon encounters were likewise reasonably paced
- Mass Attack spells seemed to have a 50/50 chance of success
- Combat wasn't too difficult with a balanced party and I don't recall struggling with anything in particular.
- I tried just about every race/class and for the most part everything seemed to work as advertised, though some combinations aren't as effective as others, which is how it goes in party based games.

Then again, the C64 had a pretty good processor and instruction set which lent itself well to gaming.

If you want to try it, you could grab the CCS64 emulator and visit arnold.c64.org for free disk image downloads of C-64 games.

I should probably point out that the 75% figure I gave assumes that the spell worked in the first place (50% chance), or that the spell is one of the higher level spells (as opposed to th 0MP spells that can fail).

By the way, this reminds me of another NES version quirk: Unlike in other versions (haven't checked MSX Cartridge, but this check should be easy), in the NES version, there's no limit on the number of times you can try the 0MP spells during battle. (In other versions, the spells will always fail if you try casting them more than once in the same battle, but not in the NES version.)

I have one question about the Commodore 64 version: How do you move? In other versons, the arrow keys (or in the NES's case, the control pad) handle movement, but the Commodore 64 doesn't seem to have a full set of arrow keys.

Ah, the days before WASD and Arrow Keys...

Ultima on the C-64 (https://www.c64-wiki.com/images/f/f9/Tastatur_foto2.jpg) uses @ ;:/ which form a diamond pattern on the C-64 keyboard. This is remapped to the PC keyboard in CCS64 so that you use the keys [ (left bracket) for up; (semicolon) for left, ' (apostrophe) for right, and / (forward slash) for down, all without shift keys.

I tried the Commodore 64 version for a bit. One thing that's very obvious: The game is *slow*. That is a rather serious issue, and a reason to not recommend this version.

Otherwise, it seems sound gameplay wise, though I did not go to Ambrosia. (I did get lucky getting a ship at level 1, and used it to get Exotics.) MP for Druids and Rangers seems to work exactly as in the DOS version.

Maybe I'll try Ultima 3 Gold, a fan upgrade of the C64 version, and see how that version feels. (Supposedly, at least the graphics code has been optimized; I hope that makes that version faster.)

Out of curiosity, what tools did you use to make your modifications? I'm curious as to what programs were available back then for that kind of thing. (These days, you can use an emulator's debugging capabilities, and can cross-assemble code from a modern PC, but you didn't have that back them.)

Quirks of Ultima 3 Gold:
* There is an intro (like what you find in the scene, if you know what I mean)
* When you start the game, you are given the option to turn on a few cheats. I have been turning on Infinite Food (the food mechanic is annoying and not really dangerious in this game) and leaving the others off.
* The game uses a fast loader. Unfortunately, this means that it needs True Drive Emulation under VICE (this is unlike the official release, which does not, and turning it off gets rid of load times). (I can see players on real hardware appreciating this, however.)
* When you leave a town or castle, there's an extra prompt, which is annoying when you're used to the original behavior.
* Saving is *slow*.
* When somebody dies, the music restarts. (The original C64 version would auto-save on character death or entering another area; this version does not, but it seems that there's still some code left-overs that results in the music restarting).
* Bug: If you save immediately after entering the world map, the music will disappear. (I think I remember that in the Amiga version as well.) This bug lasts until you leave the world map; if you get into a fight, music will play during battle, but will stop afterwords.
* You can only buy 99 food at a time, unlike the DOS version.
* Wizard spell G (random teleport in the overworld) does not work while riding a ship; in the DOS vesion, it does (but it doesn't in the Amiga version).
* Turning off the volume does speed things up, just like in the original C64 version, and unlike the Amiga version.
* Fortunately, unlike the Amiga version, poison is fast in this version.

I had written a disassembler which allowed me to read/print assembly (6502) instructions, and had a disk editor someone else wrote (can't remember who) which also provided disassembly listings of each disk sector if there were any. I had also memorized all the opcodes and could write code by entering numbers (true machine language) but eventually I obtained the LADS assembler by Jim Butterfield in one of the Machine Language for Beginners books. By then I had a C-128 with a memory mod so I could run an 80-column display for easier coding. After re-writing LADS to suit my preferences (I recall re-writing the source code parser to add features) I was able to mod games.

Also needed a book called Inside Commodore DOS because the C-1541/71 drive had it's own memory and for my fast-load/save I was able to transfer code into the drive which would run while the game was going. Essentially replaced the slow serial transfer of data with a very fast one. I had lots of fun with it. As for sector interleave, that was merely a matter of writing U3 data according to the required sector skips; not the default contiguous Sector 1, Sector 2, Sector 3, etc. which required the disk to rotate one or more full spins before accessing another sector.

For general purpose stuff I was able to use BASIC 2.0 which provided slower disk-based functions and drive memory reads/writes but was adequate for testing and handling utility stuff.

As far as the things you've noticed in Ultima 3 Gold, have you communicated them to the author? If it was a labor of love for them, they might consider releasing an update based on feedback.

Oh, and if anyone's interested in getting their hands on some old literature for the C64 and other computers of that time period, here's a site that has scanned PDFs of them: https://archive.org/details/commodore_c64_books?&sort=-downloads&page=4