This episode has a couple of instances of the door problem being solved by moving rocks rather than a convenient final wave of foes. It is definitely an approach that Gunslinger leans on pretty heavily and gets away with it mostly due to novelty. If a longer game or simply more games tried this same approach I am pretty sure it would grow tedious and dumb pretty quickly.
The multiplier in this game see powers not just some of the perks I rely on but also determines your XP gain, the bigger the multiplier the more XP you get and the faster you progress. This makes the few points in this game where you get free extended concentration or just a turret and wave after wave of enemies are thrown at you really high points as you push through and try to take advantage. If you have the right perks at these times you can get a pretty significant amount of progress towards the next perk or two.