Well thank god. What you call "opacity, gradients, and effects", I call "total inability to be bolded, colored, embossed, etc." Apple's and Google's emoji basically entirely ignore CSS in favor of looking, well, exactly the way they look. Styling emoji to actually fit your site's theme? Who'd have imagined?
When you set your text to be bold, that's a separate font, made by a human hand.
Browsers have a fake bold look when the font is missing, but it's not a look you want on your site. They just, well... smudge it to the right. For Emoji the fake bold look is disabled, because bold or italic emoji is just non-sense on the face of it, so they don't support weight settings.
Also, you can't set the color of Windows Emoji via CSS. They're already colored.
Because the colored glyphs use a palette instead of hard-coded colors, it's possible to assign semantic meanings or names to each palette entry and remap them. This would enable you to render a 'high contrast' version, or adjust the primary color of an emoji (for example, changing the skin tone of a face), etc.
The latter is actually a topic of concern: Most current emoji represent a caucasian or light-skinned individual, so the lack of emojis that represent other races is a problem. People are still figuring out how to deal with it.