Brings that really important thing from your graveyard back into your hand. Its uses are limitless.
Mono-green deck manipulation. Seriously, what's not to love about that? This sort of helps you dig (although you're only going to be digging a small hole) and it can trade your life for extra cards which is always nice.
See my comments for Regrowth.
Squishy elephant! This can solve a lot of problems late in the game. Giving an opponent an Elephant is usually a very small price to pay to get rid of a big problem.
Defense of the Heart
This card is so good, I'd be supportive of a ban if one were to arise. Someone will control 3+ creatures in EDH and you will either draw out a destroy card or have some sad opponents.
No blue deck likes to see this card come out. The Split Second on it is what makes it a great card since no one can respond to it.
Green Sun's Zenith
Step 1: Search for a problem and put it into play.
Step 2: Repeat until countered.
Pattern of Rebirth