The trick to Too Human is the combo multiplier. You need to get your combo meter as high as possible and to keep it there. The easiest way to do this is to master advanced attacks such as Slide attacks and air attacks.
To perform a simple slide attack simply hold the Right stick in the direction toward an enemy. Once you deliver an attack point the right stick towards another enemy (even if the first one is not dead), you will slide towards the next enemy and deliver an attack. Quick pointing the right stick towards your next target. This quick movement makes you a hard target to hit and allows you to quickly clear out a room filled with enemies.
What I do when faced with many enemies, I will first get rid of ranged enemies. I will slide attack towards them then perform a Juggle attack (double tap right stick) to launch the enemy in the air, then jump (A) and then press the right stick again to perform an air attack and finish them off with a Fierce attack by pressing both the right and left sticks towards the enemy at the same time. This will destroy all but the most powerful enemies in one shot. Once I land, I will slide attack towards the next ranged enemy or slide attack everything that is left.
When in trouble you can use a Ruiner. Ruiners are powerful attacks that will knock down every enemy that surrounds you, but will drop your combo meter by a full notch (still better than dying). Here is a trick, perform a slide attack before you perform a ruiner and your ruiner will only cost half a notch of your combo meter.
Also roll instead of walking. Rolling will neutralize most attacks like missiles and trolls hammer slams. But rolling will also stop you from losing health. Some enemies will zap you with stuff that quickly drains your health, but if you roll you will not lose any health points. Keep doing this till the effect is gone. Also rolling is a faster method of traveling than walking or running.
Hope these tips help. For the record, I died close to a hundred times in my first play through, but only about 20 times in my second turn, and less than a dozen times my third try and I only died twice in my forth play so far.