At face value the ENTJ and the INTJ are very similar. Both types have a love of complexity, both are intensely logical and both have a relentless, restless drive to change things, make them better and for closure. However the E vs I dichotomy makes such a difference and means they tend to inhabit different worlds.
The ENTJ inhabits the external world of people and situations, drawing energy from interactions and will love being loud, visible and will have (extremely strong) opinions on almost every subject.
The INTJ inhabits the internal world, detached and independent of thought and action, and they tend to keep it all inside until they are ready. Their need for privacy and independence means they will be quite reclusive, working behind the scenes to reflect, build and solve problems. The ENTJ is far more ‘out there’ loving the verbal sparring and robust debate and keen to make their point. Don’t ask the views of an ENTJ unless you are prepared for a bone-jarring honesty.