|Does it look real? Not particularly. Does it look cool? Hell yea!|
If you have a solid grasp on all three of these concepts, then you'll be able to make spectacular looking FX.
As I said, unless your engine supports fully 3D fluid simulation, all you have to work with are 2D planes to create your FX. So you need to trick people into thinking that the effect is still volumetric. There have been some technical advancements to help you achieve that.
Since particles are 2D planes, when they intersect with objects they would create a very obvious line, ruining the effect. It's possible to hide the line by creating many more particles, but that's inefficient and not at all an ideal solution, hence why Soft Particles were created.
|With and without soft particles.|
|Note how the pink glow from the explosion can be seen intersecting with the statue of Lenin.|
|Turns out you can have too much of a good thing.|
Using fewer particles that have a more specifically designed texture is the best way of achieving volume.
Now when I say Texture, I'm not referring to the actual textures you are using in your particle (though those ARE an aspect of the particle's overall texture) I'm talking about the level of visual noise and fine detail in the effect.
|An effect with a HIGH amount of texture.|
|An effect with a LOW amount of texture|
|I can tell there's an explosion going off, but I can't tell what it looks like.|
A game like Company of Heroes, on the other hand, has highly specialized particle textures. They have multiple different types of bursts of sparks, jets of smoke, thick debris, thin debris, etc etc etc. It's more work, but it allows them to really sculpt out the look of the effect.
|Men of War. This game came out in 2009?!|
Motion is all about how the different elements of your effect move. Motion is the biggest contributing factor to how an effect 'feels'. You can make things feel impactful, flowing, crunchy, pillowy, etc. Feel is a very vague concept, but there is no question that it exists, and trying to get control over how you want something to feel is the biggest challenge in VFX.
Offsetting elements by a fraction of a second can be the difference between a weak effect and a powerful one. Notice in the image above how the first element of the effect is a large vertical flame, then the shockwave, and only after all that does the dust cloud kick up. It doesn't happen all at once. This progression of elements in the effect makes it really feel like the explosion is ripping the ground up from the earth.
|Making an effect expand quickly, then retract helps add punch.|
Bad motion is instantly recognized. It will make your effect feel bland, awkward, or unfitting. Spawning everything at the same time can make it feel abrupt. Not giving the effects a unified motion will make it feel like an obvious simulation. People won't become interested with the action onscreen if your motion is boring.
|It's supposed to be an explosion, but it just doesn't feel like one.|