The beauty in Reign in Blood is that it doesn't really test your patience. Its very easy to listen to all the way through every time, but still has the musical value to be enjoyable. Some may argue that this depreciates the value of Reign in Blood, but they'd be wrong because it causes you to do exactly what I think Slayer wants you to do; listen to the album front to back every time.
I'd probably agree that Raining Blood and Angel of Death are two of the strongest tracks on RIB, but there is definitely plenty more to enjoy there. Its kind of brief, but that itself kind of adds some mysticism into the equation. The individual songs aren't going to continuously elaborate on ideas, but they are quick, to the point, purposeful, and the riffing is solid. I think the album as a whole is relevant enough to send the same message as eight 3-4 minute tracks, though. I'm not sure what my favorite Slayer is, but its probably either Reign in Blood or Haunting the Chapel. Both are brief but great.
Also, I agree that live Slayer recordings are better than studio. In some cases its the energy or presence, and in other cases its the fact that the live recordings have better production than the dated studio recordings. I love the live chemical warfare track on Soundtrack to the Apocalypse Disc 5.