It's happy indeed, because, in doing so, Jesus defeated the devil — He defeated death and brought salvation to mankind, who is broken and imprisoned by a fallen nature — by sin.
And, what's behind Jesus' suffering? It's His holy and pure and true Love for mankind!
God, Jesus, wants us all to be happy at Easter and always — happy and grateful for His suffering and agony, which at it's core is: to be happy and grateful for His unsurpassed Love for mankind — for each one of us!
–Helder