Leather and Steel, and what's changed from Strange Gift

TLDR; A lot.

Leather and Steel is not a paranormal game. The theme of Leather and Steel is that you are encouraged to have sex with other women by your wife, who will want to hear about your adventures.

Leather and Steel has no procedurally generated characters. Each character has their own way of reacting to the things you do. Different text, different pictures, different game results. They have different kinks. 

In general, there is a full screen render for almost every significant game action, and unique to doing that action at that particular location. Both Olivia and Chloe have three different sex scenes and multiple sexy scenes short of sex (spanking, blowjobs, etc.) and all of those have multiple renders and unique text.

Leather and Steel has fewer turns in a day -- 3, instead of 6. It lasts fewer days, too, although it is likely to get longer as more content is added.

The flirting system has changed -- you no longer spend time guessing how to flirt, although your first couple of times talking with a girl you might hit a wrong note. There is no longer a punishment for focusing on one girl and flirting with her repeatedly. Actions like flirting, hugging, and kissing start becoming less effective at some point, and non-effective a later level.

"Shyness" and "Trust" have replaced "Lust" and "Submission." Shyness goes down as a girl does things, and particularly as they do things in public, whereas trust goes up as a result of Spanking and Sex.

You can move around more freely -- as in Bondage Island, you can check out every location before deciding which girl to engage with.

"Spells" and "Rules" have both been taken out. In 0.1, the girls don't enter into D/s relationships with you, although that too will be added back in some future version.

Several locations have been taken out of Leather and Steel. Most of them will be added back in future versions. Scaling back on locations, the number of girls, etc., has enabled me to produce higher quality content. If a scene didn't add to a good experience playing 0.1, I took it out, even if I intend to put it back later. For the most part, that means that things that distract you from the things you need to do to do well at Leather and Steel are not in the game, although I felt the Mia Sunscreen scene, for instance, was entertaining enough to leave in.

This is only a partial list, but hopefully it gives you an idea of what to expect as you play, if you've played Strange Gift.