Sailor Moon S is about the quest for pure hearts and defeating Professor Tomoe and the Witches 5. The first half of the season features the introduction of Sailor Uranus and Sailor Neptune. They are on a quest to find the pure hearts so they can save the world from eternal darkness. The second half includes two more sailors, Sailor Pluto and Sailor Saturn. Professer Tomoe is Saturn's father, Saturn is a very weak girl with special healing powers. In the end, good prevails over evil. And the sailors win their fight against evil.
My opinion on how Irwin dubbed SMS is that they did a much better job than DIC. Some of the character's voices have changed, but we couldn't prevent that. Serena's voice has changed from the previous two seasons and it tries to be too much like it's predecessor and fails. Jupiter's voice is the same. Mercury and Venus both have changed, but they're fine. The voice of Mars and Tuxedo Mask has changed once again, but sounds very similar to the first season. The voices of Uranus and Neptune each fit their personalities very well. We all know what DIC did to the first two seasons, but without them I wouldn't have the slighest idea of what Sailor Moon is. I feel that Irwin does a better job dubbing and keeping it more "true" to the original. They also included the original music which is a plus. Irwin also dubbed Sailor Moon SuperS which maybe we'll get to see in the near future.