Personally I understood a cockroach flashlight as something that will work, no matter what happens.
Fenix E01 is a great example.
Preferred design patterns (in my view):
- User-replaceable battery
- Long runtime
- Highly reliable
- Simple design (less is more elegance)
- Graceful degradation (e.g. no sudden death, battery vampire)
- Foolproof user interface (e.g. no high mode that can drain the battery in 30 minutes)
Bonus points for:
- Modular design (think mixing parts of SureFire / SolarForce P60 system; or mixing Fenix E01 and Sofirn C01/C01S tubes and heads)
- End-user repairable
- Running on safe, robust and long-life rechargeable cell chemistry (LSD NiMH or LiFePO4)
If you are willing to broaden your cell size and chemistry beyond AAA, there are some other interesting options.
Personally I like the 9V Pak-Lite (warm white version, or modded with Yuji 5mm LEDs).
Back to the future of flashlight history, and still being produced 
Extremely simple and reliable design: only components are 2 LED’s, a switch, and two resistors.
Runs great on depleted 9V batteries from smoke alarms.
Perhaps the ultimate bomb-proof light is a driverless CR2016 or CR2032 coin-cell light with a 5-mm LED; either fauxton or Photon.
Or an old-school xenon-bulb P60 light.