Have a slut mode where you can make out with monsters without having to worry about health.

CG gallery  (if there are any)

Make sex a reward. Don't reward failure.
My idea:  Grab enough items to earn a sexy scene.

Weapons with multiple effects.

"quick-time event system where she needs to orgasm before the enemy so as not to lose any health"

The H game, "Unholy Sactuary" has good mechanics.

People are tired of Toonpimp-style escape rape via button-press.

Avoid:  "get touched by an enemy = get raped"
(girl struggles befoer rape)
(Enemies remove clothes)

Multiple endings.

A gameover ending. See the end result.

Sexy concepts are important. But pictures are a plus.

Porn is the main draw, 
so there needs to be a lot of it.
Otherwise we just go play Super Metroid.

Give sex variety in poses and actions.

Large sprites, as long as they look great.
(Too large tend to look ugly)
Facial expressions.
Nipples.
Clearly female.
Zoom-in on sexy animations.
Red hair. (Some people are tired of blondes.)
Avoid making the breasts ridiculously huge.

Player costumes.
My idea:  Armor falls off during rape. Pick it up to regain defense. Without it, you have very low defense.

Avoid gore.
Avoid instant-death traps.

Enemies based on moster girl encyclopedia.
Succubus, catgirls
Tentacles instead of spikes.
Maids & Nurses.
Monsters instead of sexy female enemies to change things up.
Forced mouthfuls + swallowing.
Give enemies variety in gender and style.
Sometimes bestiality.
