This is a nice character episode for the doc. He falls in love with a female patient, whose brain has been transferred to the computer and is now projected as a hologram while the doc tries to save her real body - which is blemished by the phage and about to pass away unless the doc finds a cure.
The doc though is unexperienced (or shall we say "not programmed") in matters of love and acts quite wooden and unromantic. With a little help of Kess and Paris though, both find a way to each other and the doc shows a more empathic side of his. What I don't like about this episodic approach of Star Trek though: It is always this "Once and never again" scenario. Of course doc's love interest has to leave him after the treatment to help her people. It would have been much more interesting if the crew would make friends that enrich their own story arcs and change things on the ship.
Also what is strange: Data is said to be a sentient life form. He is aware of himself, he thinks and is able to adapt. The doc on the other hand is also aware of himself, he also thinks, is able to adapt and unlike Data obviously capable of having emotions. So he is even more human than Data! The only thing missing is a body. He is just a hologram. So, why is the doctor not treated like a sentient life form? How comes he is just forgotten, when the ship is evacuated like in another episode? Shouldn't the crew treat him like a living being, too? Just like Data? We talk about an intelligent computer program that is able to learn, evole and adapt. This is not different to a human's brain.