Um, yeah, all you need to do is go to any gathering of nerds to find the answer to this question. Although the original series bombed when it first debuted, it became a cult phenomenon in the years that followed. Emphasis on "cult." As evidence of their dedication, fans single-handedly got the Star Trek film series made based on a letter-writing campaign.
Most Trekkies consider The Undiscovered Country to be a solid entry in the original film series, even if it doesn't reach the same heights as The Wrath of Khan or The Voyage Home. Legit Trekkies see this as evidence of the famous "even-odd" curse on the original series: the even-numbered films rule, while the odd-numbered ones drool. Science.