I've been really enjoying this set, it seems a bit slower and more complex to me than the last couple. All the colors except green seem decent and even the aggro decks need a lot of synergy to function well.
I went 7-1 with this Dimir Descend deck on the back of [[Aclazotz]] and two Uchies. The playset of [[Echo of Dusk]] was really good - turns out a 2 mana 3/3 lifelink is pretty dece.
It's pretty fun so far. There's a lot of... depth, and a bunch of different interesting archetypes. Some cards seem (particularly caves-oriented ones) seem like they're fairly ineffective at what they want to be doing, though. I hope I'm wrong about that and I just haven't found the right way to build those decks.
I think you are right and caves are just a trap and not worth it. Maybe with two of the red cave sweeper and two of the lifelink leech there is a chance but anything less than that is just not worth it. I'd love to be proved wrong though since new land types are cool.