These are some great lands that came out in Shadowmoor (except Graven Cairns, which came out first in Future Sight). Why are they great? They're mana acceleration and mana variety in land form that doesn't come into play tapped (like Arctic Flats), require you to sack or bounce lands (like Lotus Vale or any of the Guild lands), or hurt you (like Grand Coliseum). As a first turn drop, it's not the greatest, as it can only produce colourless on its own. but from turn 1 on, it's awesome. It not only doubles the mana produced by a single basic land, but it can diversify it as well. If you only have an Island and Sunken Ruins, you could play Counterspell, Countersquall, or Dash Hopes. It gives you tons of options in land form, so it's fairly safe from destruction as well as being free to play.
Pros: Diversifies mana colours, doesn't enter tapped, bouncy, or painfully Cons: Not very useful without the right start-up mana Rating: 4/5