It´s basically the same mod for SR3. It has some cut content, bug fixes and the like. It changed my gaming experience drastically :)

Yeah, GoS was done by idolninja as well. But GoS is smaller then GoTR. Gentlemen of Steelport contains fixes as well as the option of extra colours (such as the saints purple from sr2) and that you can have the radiostation on a tank.

I didn't really notice any bugs with 3.

Hmmmm.
I'll try it eventually. First I'd like to play Mass Effect so that I can play SR 4 and get all the jokes.
THEN I might go back to SR 3, but shit, I might be dead by then.

And for the people who play Skyrim: You should check out the Beyond Skyrim project. It will blow your head off.*



*literally. Sorry, if this warning comes too late.

I'll second several that have been mentioned already:

Nehrim (for Oblivion) and Enderal (for Skyrim) are amazing total conversion mods that I'd consider just as good (if not better) than the original games they're based on.

Fall From Heaven II for Civ4 is another total conversion mod that changes the setting for the game into a dark fantasy world; it's probably the closest thing out here to a more modern Master of Magic.

I also really like The Long War Rebalanced mod for XCOM. It's a further modification of The Long War mod (which extended and added a lot of depth to the original game). Some of the overall changes I liked the most were changes to pod mechanics (pods trigger other pods in visual range, resulting in some large firefights but meaning you can move aggressively on pods without worrying about triggering more of them), as well as balances to health and damage reduction mechanics that really shifted the focus more heavily to tactics than being RNG heavy like the original game and to a lesser extent the original Long War mod.

Starbound is absolutely lifeless without Frackin Universe. (described here).

What's so nice about it, is that it's all found on github so updating is easy.

The Sims 3 is pretty amazing, but a lot of the code underlying is whack. Nraas mods help solve a lot of the problems, making playing Sims 3 a lot more sane and allowing longer lived save files.

Edit: Do source ports and engine conversions count too? Because I couldn't think of playing vanilla RCT anymore.

Venom Mod for Return to Castle Wolfenstein. By far the best one I have ever encountered. No other mod has increased my enjoyment from a game more than this.

Doom has so many cool mods and fanmade campaigns you could play nothing else for a good long while, some of these really change the core gameplay to the point its almost unrecognizable.
Brutal Doom gets mentioned often, some people recommend Project Brutality over it, I dont have much playtime in either.
High Noon Drifter is an incredible weapons pack/character mod with a low-tech weird west theme, in the more arcadey end of things Demonsteele is basically Devil May Cry in first person while GMOTA is an incredibly fun medieval beat em up.
Russian Overkill, Guncaster and Trailblazer, all made by the same dude are stupidly fun and stupidly overpowered, play them with enemy mods or in maps with TONS of enemies. (Colorfun Hell for example)
There just SO MANY, Space Hunter is NES metroid in Doom, Metroid Dreadnought is more inspired by the Prime series.
And lets not forget Hideous Destructor, its basically the best approximation of a realistic military shooter you could have in the Doom engine (with demons), its not everyone's cup of tea, but if you are into masochistic military simulations you should totally give it a try, just read the manual.
FinalDoomer is not just one, but several weapon mods rolled into one, each one specifically tailored for a different mapset, but you can use them in anything you want.

And then you have like 20 years of maps to use these in: some standouts are Scythe 1/2 Ancient Aliens, Sunlust, Back to Saturn X 1/2, the list goes on forever.

Also Death Wish for Blood, there arent many projects for that game but this one is just stellar.

Arcane Dimensions for Quake 1. Amazing campaign mod that should be an official release:

http://www.simonoc.com/pages/design/sp/ad.htm

F3 with FNV controlled by TTW.........Skyrim...ForgottenMagic-Redone.

Oh! I'll check that out and use it to test my wireless mouse i've got coming in. Much thanks!

BMS Falcon mod for Falcon 4.0

EECH 1.16 mod for Enemy Engaged Comanche vs. Hokum

WoV 2.13 mod/update for Battle of Brittain II Wings of Victory

The Pacific Air War and Desert Air War mod for The European Air War (and many more)

1955 GP mod for Grand Prix Legends (and many more)

RBR 2017 mod for Richard Burns Rally

Power & Glory mod for GT-R 2