
Even if you give it a shot and end up hating it, it's worth trying for sure. This mod is my absolute favorite I've spent more time with it than any other game in my library. There are a lot of cases where unit balancing has been amplified meaning some units will truly get steamrolled against others whereas in the vanilla game it'd be more pitched. Some of the campaigns (I'm thinking the Crusader States or Lithuania) are pretty damned difficult if you don't know what you're doing. Having a basic knowledge of tactics, and what unit types work against each other, can make it so SS doesn't overwhelm you. Stainless Steel has the same settings that the vanilla game (Easy -> Very Hard), though I'd say it'd help to be at least competent at the base game before you jump in.

No idea what you mean by this, could you elaborate? There are some that doubt the CAI can be fixed at all, but I feel it's better if only because of the diplomatic improvements. Campaign AI may or may not be improved I honestly can't tell sometimes. From what I can tell, alliances hold better in Stainless Steel, and diplomatic alliances can truly be an asset (whereas in vanilla they're basically a non-aggression pact).

There are three campaign AIs to choose from: a highly aggressive setting, a more peaceful setting, and a strong balance in between the two.

How good is the campaign and diplomacy AI?
