The best part for me is messing around with different skill combinations. Runs do not always hand you the same upgrades, so there is less temptation to repeat one tired build. Once the enemy count starts piling up, placement and timing matter a lot more, and one bad defensive decision can unravel the whole lane.
Damage multiplier, God Mode, unlimited skills, ad removal, and game-speed options are already unlocked in-game, which cuts down the grind considerably. The roguelike setup works well for anyone who enjoys tower defence but gets bored when every run follows the exact same script.