Well, I think there are many similarities in the Amiga and Linux approaches. To look at the citeria the OP mentioned:
- Transparency: Definitely "yes". You can ultimately examine every single aspect, every file, every function of the OS and its components, everything comes with full source code (if you really want to go that deep). There are thousands of communities and tons of documentation which help you in doing so.
- Power: Absolutely. There just is no example where Linux can't be used.
- Simplicity: Yes and no. It might be quite a learning curve if you only have worked with other OSes previously. But once you have understood the basics, everything seems logical and easy. However, you rarely just throw in a floppy disk and click around ;-)
- Small code / minimal components: Yes and no. Most distibutions come bloated with KDE or GNOME and tons of crap being installed by default. So this is rather a question of customizing. Personally, I prefer window managers like IceWM or Fluxbox (and FreeBSD btw, it appears even easier and more logical than Linux to me). They are extremely fast, you can get hundreds of nice themes or just create your own. This is one of the biggest commonnesses IMHO. Ultimate configurability. You can completely modify the look of your desktop, mess with icons, all the stuff Amiga users love.
If you want to use a state-of-the-art OS, I recommend you give Linux a shot. Nothing keeps you from continuing to use your Amiga in parallel (like I do). And E-UAE runs quite nice, too.