Master of Orion 3 is just released and a lot of people have commented that it's actually decent when modded. With that in mind, which mods do you know of for MoO3 that are good, what do they change, why does that improve the game and where can you get those mods?
Here's a template to use.
Mod: Name of the mod
What: A brief description of changes
Why: A brief description of why you recommend it
Where: A URL to the mod page
Example:
Mod: The Awesome Mod
What: 30 more race picks, 26 new races, 63 new techs to research
Why: It makes everything more awesome!
Where: www.awesomemod.com/downloaditnow/download.html

Master Of Orion 3 Master Mod
http://www.moddb.com/mods/master-of-orion-3-master-mod

Link to many mod packages and unofficial patches:
http://www.moo3.at/mods/index.php?action=displaycat&catid=17

So much for the template, eh?
Anyway, *some* context would be appreciated, guys. Which are a necessity, which are just fun, and which are pointless?

This is a tough question! Look on the official forums.
But before you do anything at all a prior question comes up. Is this version released with the last official patch? Got to have that before the other mods will work.
And there may be another problem. The fan patches would not work with the Steam version or the D2D version, forget which. You needed original retail disks.
I did the full patch sequence once, but then the computer died. Nothing to do with Moo3. Started by adding last official patch. Then got a set of patches including one to improve resolution and bring the Galactopedia up to date. Then there was the Strawberry mod that had many awesome improvements. And there was a way to go without the disk in the drive, not needed here obviously. And there was other mods I may be forgetting.
Now, once I got all that working the game was fairly decent. Turn on auto colonize, figure out how to use the rally point construction. Figure out how to make fleets. Figure out everything.
Moo3 is a decent game if you can get all the fan patches to work, but the learning curve is steep like hard rock climbing up a cliff for me.
With the GoG version, though, the question remains. Will it work with any of the fan patches? If not we are doomed!

I downloaded and attempted to install the Tropical Mod.
The included moo3.exe requires Disc 2 (the play disc) from the original retail game.
I don't really have the gumption to try playing with all of the mods installed via the dll, but without the modded .exe.
I will try this at some point however, probably tomorrow. I will post the results, however dire they may be.

Keep in mind that the version of the "Tropical Mod" at www.moo3.at isn't the last version of the mod. It's only the last version that was created by the original developer. He does however, play an advisory role in it's current development and advises and helps the man supporting the "Tropical Mod" to this date.
The newest verision of Tropical is below.
Get Tropical!
http://www.mediafire.com/file/tmmdmyzykbm/UOP_Tropical_V1.3.10.zip
Tropical's forum thread at Atari
http://www.ataricommunity.com/forums/showthread.php?t=517077
Keep in mind though, that this hasn't been tested on GoG's version of Moo3.

uh-oh. That sounds like bad news for the GOG version.

Hooray.
It appears to work now.
I had to completely clean the registry, do a reinstall of Moo3, and do it all from scratch.
I can post a guide to get this mod to work, if anyone wants.

yes please, me buying or not buying this game completely depends on if at least tropical works.

Well, let me do this then. I will play a few games of this, and verify there are no show-stopping bugs that I am not expecting.
If it runs well, I'll post a guide later today.
I would rather not have you buy this game based on the mod working, then find out later I didn't do my homework and it has issues.

That would be very much appreciated! And don't worry, I wouldn't hold you responsible if it didn't work after all.
Also, take your time, I'm not in a hurry :)

Starting a new thread for this, as I'm hoping they will sticky it.

So, I am guessing they did not sticky it since I am having an issue with on of the .dll files you mentioned. I can find NOTHING to fix this problem and manually registering it is not working....