"S.O.S." isn't a perfect episode, nor is it the most eventful of "Lost" episodes nor did it come along at the perfect ime, nor is it a masterpiece of character-driven drama. It is, however, a completely pleasant, genuinely well-written gem which takes a look at Bernard and Rose, two of the few 'normal' people on the island, and certainly one of the more realistic and authentic couples. The flashback scenes are genuinely effective and involving, and even tie into the mythology (through the faith healer and the 'energy areas', one of which is the island, obviously) for those who believe the mythology is the main driving force of "Lost".
The episode is notably well-directed by Eric Laneuville, and very well-written by Leonard Dick and Steven Maeda, and as much as the plot involving Bernard and the sign he wishes to make is unnecessary, it's hardly aggravating or worth getting upset about, and is very, very far from the most annoying episode-contained storyline on the show. It's a good bit of sometimes humorous fun, actually.
The acting is excellent as well from L. Scott Caldwell and Sam Anderson as Rose and Bernard, and the scenes involving Fenry Gale are really fun to watch as well. The episode as a whole is just a really good, enjoyable episode, with an ending that sets up a superior, devastatingly good episode to come.
8/10