You totally nailed the effects when you chain the enemies. The hitstop and sounds are so satisfying; I'd personally add more visual effects, like screen flashes or blood particles from the enemy.
Also, I think it'd be better if you didn't have to necessarily chain every enemy. That way, the player not only can only attack specific enemies, but also be encouraged to actually chain every enemy, since the damage multipliers rise. High damage, but lots of time.