I really do highly recommend it, like Antares said. Give it a whirl and see what you can make!
PRE-POST EDIT: This post got huge, read on if you want to read my inadvertent introduction to Apophysis and nebula-making.If you'd like to try something nebula-like, the following settings are a good start:
Go to options (Ctrl+P)
-Random tab: 3 to 5 transforms, 2 to 5 mutation transforms, no symmetry.
-Variations tab: Check Spherical only. (Other variations can lead to interesting effects so don't be afraid to experiment with combinations of things, but for nebulae I have most luck most often with just spherical -- the other variations can tend to produce sharp boundaries which obviously don't look great on a nebula.)
Gradient: Either set to random preset if you want the program to randomly use gradients that come with it by default, or use randomize if you'd like it to randomly create new ones using the settings on the right. You'll have more control over the gradient in the gradient window (F6) afterward.
Then make a batch (Ctrl+B). Usually I use a batch size of 25, you can set under the Random tab described above. Scroll through the previews on the left and see if any of 'em suit your fancy. If not make a new batch.
When you find one you like, you can manipulate it using either the triangle editor (F4) or the mutation editor (F7). New users will probably find it easier to use the mutation editor at first, but the triangle editor will give you far more control over all aspects of the fractal. For nebulae, I tend to use both -- I start with mutations to more easily get a nebula-like flame, then use the triangle editor to fine tune it to my liking.
Mutation Editor: Set the speed low (0.5 to 0.15, perhaps), and make sure the trend is set to spherical. The default is random which will do god-knows-what to your fractal. Then the way the mutations work is sort of like artificial selection -- you'll see 9 previews of your fractal, the center one is the way it looks currently, while the ones on the edges are after applying some randomization to it. If you click the center image, it will keep the fractal the same and make a new set of mutations to look through. If you see one you like, click it, and it will make that change and create a new set of mutations. In theory, if you keep clicking the mutations you like, your fractal will gradually become better. In practice, this sometimes works really well, and sometimes it just never seems to cooperate, as if every possible mutation makes the fractal worse. And don't freak out if you click a mutation and don't like the change it made. Just hit the undo button. If your experience with Apo is anything like mine then you'll become best friends with the undo button very quickly.
Triangle Editor:
If you're giving this one a go, then good for you. It might look very intimidating at first, but I guarantee if you stick with it the results will be worth it. Unfortunately there is no way I can make a tutorial for how to make a better fractal this way -- you simply have to experiment. What I
can do is tell you what the features are and how to use them.
-The big black grid: Each transform is represented on the grid as a triangle. Expand, contract, drag, or rotate a triangle, and the fractal will change accordingly. With practice you may start to get an intuitive sense for what kind of adjustment will do what kind of change to your fractal.
-You can add, copy, or remove triangles to increase or reduce complexity.
-The 'Weight' of the transform determines how much that particular transform will factor in to the overall shape of the fractal.
-Triangle tab: A different means of manipulating the triangles (as opposed to clicking/dragging on the grid) -- this tab treats a triangle as an entire entity.
-Transform tab: More means of manipulating the triangles -- this tab treats each point of a triangle individually.
-Variations tab: Allows you to directly control how much of each variation goes into each transform.
-Variables tab: I don't suggest messing around in this one -- that's for very advanced types of fractals.
-Colors tab: Gives you a huge amount of control over how the color gradient is applied to each portion of the fractal.
-Xaos: I've never messed with this, I don't know what it does exactly.
That's it for the triangle editor, the other two important editors are:
Adjustment (F5): I think this one is pretty self-explanatory when you look at it. One thing that might not be so obvious is the relationship between
scale and
zoom. Basically, zoom doesn't affect the overall quality of the fractal. Scale does. So it's a give and take: If you want to expand the fractal, increasing the zoom will increase the amount of detail, but will also increase the rendering time. Scale will expand it without increasing the rendering time, but will sacrifice the fine detail.
Gradient (F6): This controls the color. You can select a gradient from the presets or make your own, either randomly (right click the gradient, select randomize -- this uses the settings under the options > random tab), or make apophysis create one from an image by 'blending' it (the smooth palette button at bottom right). You can also adjust the hue, saturation, contrast, etc of the gradient in this window. In short, you can do a lot here. There's no excuse for not having a kickass gradient to go with your kickass fractal.

Lastly, the
Render Tab (Ctrl+R): This is also fairly self explanatory. You can control the size of the render, its quality (higher quality = more rendering time!) and the format of the created image (you can even save it as .png with transparent background -- great for editing it further in GIMP and the like to make a nebula!)
One last thing -- before rendering a fractal, try hitting F3. This will very quickly draw up a render for you in fullscreen. You can hit F3 again and again to render more and increase the detail. Great if you really want to see the fractal in high detail before investing the time to make an actual render.
That's it. Good luck and post results!
