This seemed like a VERY hard task, getting to the final level, sitting in the overseers chair, but its actually quite easy with the right set-up; Techie.
As you begin your run you have the choice to pick between 1 of 3 "classes", each with slightly different setups. Unfortunately you are looking for the one class to ensure victory, and if it doesnt show, do your best and try again. Why? 6 shots on, say assassin, hurt a lot, and not all floors offer healing. 6 shots on Techie mean you hide for 15 seconds.
The Techie starts with -20% health (the only class with a negative, easy to spot) and +20% energy. Whats more is their starting enhancement is a recharging shield worth 25% of their energy.
Energy is the cheapest stat to level. As of writing this, 71/100 energy costs me just over 2k credits. Every other stat is 20 and costs the same.
With this in mind, run through as far as you can for credits, upgrade damage/health/slots a few times (I only needed 15/15/5) and dump the rest into energy. This effectively makes the game as "easy" as a twin stick/bullet hell can get.
Final tips;
"Omnitech floor bonus", an enhancement found chapter 2 (after defeating Shelob, boss 1) gives the player 100 credits per floor number completed, min 500. Costing 300 at game start, simply getting past F1 nets an extra 200, with 500+ profit each floor after. Cuts farming time regardless of skill.
Speaking of floors, getting to the green (purple is special level) elevator ends the floor regardless of enemies left, so run if you need to. Just dont expect the option to run from any of the games bosses.
Explosions hurt you. Duh, yeah, but even your own grenades, micro missles and such. So NEVER idle if the floor under you has a red circle.
Enhancements to energy will boost the power of your shield. You want those and any that offer healing (currently I found 2, 35% per floor & 15% of energy pickup)
Lastly, each boss you beat opens up a new elevator to start a run, skipping 3-5 levels. Make sure you bulked your stats if youd rather start on a higher floor (less time to overseer, fewer gear & enhancement drops)
I hope this helps. It was a hard game before I found this out.
Happy Hunting (>*_*)>