Untapping lands lets you play more stuff. Playing more stuff is fun. One might say that the casualness of this all depends on what the other stuff is, but isn't that just as true of Liliana's tutoring? And token-generation is pretty cool. On the topic of being able to build a deck around a card, I'd say it's not his strong suit. But who builds a deck based entirely around Shriekmaw, Brion Stoutarm, or Goatnapper?
As for Sarkhan Vol, I don't know whether to hate him for ripping off Fires of Yavimaya, or love him for for being a legitimately awesome planeswalker take on an old standby enchantment. It's his ultimate that's key, really. Garruk's is a cool bonus and a dangerous finishing move, especially for green. Liliana's is about as flashy and impressive as you can get, but also expensive. Sarkhan Vol, though, has an ultimate that says, "I hate you and you are going to die now." It's as though all the spite from every beatdown player ever losing his army of creatures to a control deck has coalesced into a huge, screaming mass of draconic vengeance.