I remember thinking it was a real shame to have Tasha leave the series. She was one of my favourites, moreso because we didnt get to see her in action against the Borg and later enemies.
Still, her screendeath makes this episode an automatic classic Though the location of the planet is awful compared to later sets (i think its the one from an earlier Q episode). That aside, there is for the first time a real feeling of foreboding. The shock of losing one of the crew so early just reaches into your resolve and tears it out for all to see until the end. Picards parting words echo with a good deal of resonance, but it is Tasha's farewall holo-goodbyes that will bring a tear to your eye.
Action scenes vary quite well and have stakes upped at the right time and with Troi in constant danger, the feeling of desperation is clever sown into the plot as the danger presented get more real with every encounter.
The alien is perhaps the first that carries are real sense of evil purpose, which is why this episode works so well.
7.5 just doesnt do this episode justice. You however, may feel that my score is too high. If you do, I dare say youll probably think of somethin inbetween both!