1. it's a very realistic portrayal of sci-fi – spaceships have velocity, there are no aliens, nukes are the most powerful weapons, the fleet runs into supply issues, there's politics hampering the military.
2. they're exploring some deeper issues very well: how people react during the after math of a catyclism, whether the humans deserve to survive, robots becoming sentient (cylons are robots created by humans), what's justifiable for the military and politicians during a time of war, and ultimately what it means to be human.
3. right now is season four which is definitely the last season, meaning the show will be wrapped up. Hopefully all the mysteries will be tied up saitsfyingly and I think the creators have the guts and talent to do it. This isn't a show that will go on for ten seasons and never get any resolution (one complaint about star trek).
4. some really strong characters / actors, my faves are Admiral Adama, Starbuck, Tigh, and Baltar.
5. There are some truly awesome episodes where everything is flipped around bringing definition to the words “WTF?”

Make sure you rent season 1 with the miniseries included, as there's a surprise at the end of that one.