Difficult choice!
I've only seen season 1 (thank heaven for DVDs!), and have been trying not to read too many spoilers for later seasons before I actually get my hands on the episodes...
I'm probably not going to find much agreement here, but I'll stand by my opinion that Fire and Water had significant concept potential. Granted, it could (and probably should) have been better developed and implemented than it was.
The series seems to be making some subtle but important points with some of its concepts, the most significant of which I think was in There But For The Grace Of God. The sentimental "practice random acts of kindness" bumber sticker motto may seem trite, but the whole alternate reality concept in this episode seemed to illustrate that little bits and pieces of compassion, understanding, patience and communication can have a real impact. Past hurts, miscommunications and misconceptions can snowball quickly into a real mess! And the presence of each individual finding their balanced niche in life can make a real difference, not just to them but to the people around them and society as a whole.
A few of the season 1 episodes seemed particularly well done to me, both in concept and implementation. Children of the Gods, Torment of Tantalus and In The Serpent's Grasp stand out, but I've watched the whole boxed set (and the special edition movie) multiple times now.
The costuming in the pilot was awesome, but I'm really partial to both Minoan architecture and studies of neolithic paleontology, so I loved the sets and references in Broca Divide.
Lots of particular *scenes* stand out from the first season, but deciding on favorite episodes is pretty difficult!
-- Adele