The reason Thoughtseize isnt fun is because it just isnt a card you can interact with on any level (in Standard and to a lesser extent in Modern)
It's best combined with cards that create token creatures when you cast spells, as it'll give you a large number of creatures to attack with
As a copy of a permanent spell resolves, it's put onto the battlefield as a token rather than putting a copy of the spell onto the battlefield
Copies become tokens.) Enchant creature you control Enchanted creature gets +1/+1 for each enchantment you control
So, if a creature with double strike and a creature with first strike have enough damage to destroy each other, they will kill each other in the first damage step
Its definitely worth pointing out cards like The Ozolith, Vedalken Anatomist, Contagion Clasp, and Contagion Engine that can start putting -1/-1 counters on our opponents creatures as well