I've been using org-mode in various capacities for a little over a year now. I've tried other tools but keep coming back. As far as complexity goes, I feel like I'm barely scratching the surface. I like what Neal Stephenson has to say about emacs (which applies just as much to org-mode):
In the GNU/Linux world there are two major text editing programs: the minimalist vi (known in some implementations as elvis) and the maximalist emacs.
I use emacs, which might be thought of as a thermonuclear word processor. It was created by Richard Stallman; enough said. It is written in Lisp, which is the only computer language that is beautiful. It is colossal, and yet it only edits straight ASCII text files, which is to say, no fonts, no boldface, no underlining. In other words, the engineer-hours that, in the case of Microsoft Word, were devoted to features like mail merge, and the ability to embed feature-length motion pictures in corporate memoranda, were, in the case of emacs, focused with maniacal intensity on the deceptively simple-seeming problem of editing text. If you are a professional writer – i.e., if someone else is getting paid to worry about how your words are formatted and printed – emacs outshines all other editing software in approximately the same way that the noonday sun does the stars. It is not just bigger and brighter; it simply makes everything else vanish. [1]
A few things for newbies that might help:
1. A lot of org-mode 'power users' post their workflows and all of the attendant emacs lisp code [2] [3], and many new users feel like they have to customize their org-mode experience to that level to get any use out of it. DO NOT DO THIS! Start completely fresh with a clean install, just use it as a braindump outliner, and SLOWLY start adding new features as you go, based specifically on what you need for your individual workflow (the most useful first thing to learn for most people, after basic outline creation and folding, is probably the agenda view). This way you 'grow' the program to fit your own needs organically, rather than trying to shoehorn yourself into someone else's idea of a perfect workflow.
2. One customization thing I will say you should do immediately is to change the theme to match your preferred UI style. It will make a huge difference in how you 'feel' while you're using it. I love emacs but I hate, hate, hate the default UI look-and-feel. I will plug leuven-theme [4] as my current go-to for org-mode, but also dig the sanityinc tomorrow themes [5].
I will also throw in a compliment to the awesome community around emacs. It's happened to me many times where I've encountered some shortcoming or 'missing' feature of my existing setup, thought to myself "if only I could do X and Y," and discovered after 5 minutes of Googling that someone has already written something that does exactly what I'm looking for...
[1] from 'In The Beginning Was The Command Line' (1999)
[2] http://pages.sachachua.com/.emacs.d/Sacha.html
[3] http://doc.norang.ca/org-mode.html
[4] https://github.com/fniessen/emacs-leuven-theme
[5] https://github.com/purcell/color-theme-sanityinc-tomorrow