I definitely have a soft spot for Dead Winter Dead, which only has a few weak tracks. The Wake of Magellan has higher highs but also some lower lows. Morphine Child off Poets and Madmen is like a concept album into itself.
In terms of obscure concept albums, Murder by Death's "Who Will Survive, and What Will Be Left of Them" is also great. It doesn't work too hard, has some great lyrics (like the song about people turning into pillars of salt and falling apart and the track about child zombies). It's basically about the Devil coming to a small desert town, being betrayed, and murdering most everyone. "That Crown Don't Make You a Prince" has an epic cello solo too.