An omniscient third person point of view (POV) style means that the narrator knows everything that is happening, even inside the characters' heads.
All readers are looking to feel strong emotions when they read fiction. The particular emotions they expect may vary from genre to genre, but a story that doesn't create any emotions in its readers will feel boring.
Because the narrator has so much power to create emotions in your readers, the narrator voice needs to be both interesting and invested in the outcome of the story. This can be harder to do when the narrator is outside the story.
For this reason, there tends to be less omniscient narrators in recent fiction, but that doesn't mean an omniscient narrator can't work for your book.
The key to a good omniscient narrator is to avoid being clinical or distant from the story. The narrator should have a distinctive voice and should be emotionally invested in the characters and plotline.
Two good examples of an omniscient narrator with a strong voice are The Book Thief and The Series of Unfortunate Events. In one, the narrator is Death personified and the other is narrated by a dramatized version of the author. Both do a good job of having a distinctive voice while still being outside the events they are narrating.
If you want to write omniscient POV, you’ll want to practice flowing naturally from each character’s thoughts, picking your details strategically, and providing someone or something for your readers to focus on so they don’t get overwhelmed.
In omniscient POV, you technically only have one point-of-view character, your narrator. Everyone else's thoughts are presented to the readers by that narrator. The story can move to follow any character at any time, as long as the narrator clearly establishes the time and place of the scenes as they change.
Make sure that your narrator is guiding the readers through the various characters' heads, rather than showing them everything all the time. Readers should never be confused about whose thoughts they are being shown. For clarity and pacing, usually only one character should react to an event before the story moves on.
Omniscient POV is great for connecting a story over large times and places. It's a good way to show how events effect a lot of people.
Omniscient POV doesn't work well for character-driven plotlines or romance novels, where tension is best served by limiting what readers know and sticking close to specific characters.
If you aren't interested in creating a distinctive narrator voice for your book, you may find a limited third person POV works better for you.
For more thoughts on how to choose the right POV for your book, check out this post.