Unfortunately the Tyranids dont feel, and well theres just too many of them to count, not even Isaac can destroy them all, they just spawn to quickly for his uber prowess.
"Lebensunwertes Leben." Isaac said, and purple arcs of lightning, like those in a plasma lamp, took the life-force from the Death Leaper attacking Keegan, and transfered the minuscule amount of energies to Isaac through his hands... He then engaged the main force in melee combat, as Devourers and Fleshborers fruitlessly smashing hemselves against his compressed Infinisteel armor, Isaac cut down Tyranid forces one after the other, and many of them died against the ravages of his hatred itself. Isaac was indomitable, but he was only one man, and one man can only do so much against an entire army.
Keegan was now brimming over with anger, his ammunition stores becoming seemingly infinite as the weapons he weilded started feeding off of his now inexhaustible levels of malice. A once valiant soldier becomes a heartless man of war, gleefully shooting down Non-Humans, such as men like Ted Vorurteil, and now Frank Keegan.