Let me discuss, from 21 years experience with tex/latex, some of the pros and cons. I will try not to make too much of the fact that I would never use anything else. After all, I have 21 years of experience to call on.
Cons: There is no getting around the fact that it is hard to learn. You must buy one or several books since there is little online help (although the source for the texbook is available, but it is supposed to be used only for examples).
It is not WYSIWYG. You have to first edit, then compile, then view.
The error messages are, not to put too fine a point on it, feeble.
You provide your own editor, although there are free ones available.
The font choices are, unless you choose to pay for them, limited.
Pros: The output is superb; I have published three books using it and you simply do not notice they are generated on a microcomputer. One of them is available for free download; anyone who would like to see it may email me.
Everything I have written in the past 21 years will still compile; the current version of 1989 was basically a bug fix (with a couple minor features added, mainly to accomodate foreign languages) of the 1982 version. Try loading a ten year old Word file.
Although it handles any text well, it is optimized for technical, especially mathematical, work.
It is trivial to convert to ps or pdf output. There are html converters, but I have never tried them. For web posting pdf is the way to go.
You provide your own editor, although there are free ones available.
It is available for every computing platform I am aware of.
There is no cheaper program available. (It is absolutely free, although it is possible to buy it along with considerable hand-holding.)
That’s all I can think of for a while. I would recommend it for someone who will be using it for long enough to make the learning curve worthwhile, but not as a one-off project.