In response to the question on the story in Acts...

The couple wasn't struck dead because they didn't give enough money, they were struck dead because they lied about the money they were giving. They tried to look fabulous by saying they gave all, when they really did not.

And as for the God of the New Testament being sweeter than the God of the Old Testament... They are the same God. Just as sweet as He has ever been. There is still discipline, there is still judgement, there is still mercy, there is still grace. God in His infinite wisdom doles it out as He sees fit.