It was a suicide mission Merle knew that, and so did we but it was so depressing to see him losing his finger and getting shot by the Governor (Philip), but the worst part was..
Seeing Merle as a walker and Daryl having to kill him. The two brothers.
Despite what he did to Maggie and Glenn, it was under the influence of the orders that the governor gave him.
If someone I loved turned to a walker, I couldn't bring myself to put an end to it, it'd just be too much on myself.
P.S.: If Andrea had killed Philip when she had the chance none of this would have happened. He deserves to die for everyone that he's murdered.
It's Daryl's duty to kill the governor now for what he did to his brother!