I thought Merle had some military experience. In an ambush situation, your intended target should be your first shot, so you don't give away your position before achieving your objective. Unless your position is secure and you can complete your mission despite your location being known. His location was far from secure, seeing as a walker managed to draw him out of hiding.
Of course I know this is TV and the villain has to stick around until the end of his arc. But it just made Merle look like a screw up instead of someone with military training.
I don't see it that way. He never expected the Governor to be on the front line when his plan went into motion. The Governor wasn't his intended target. Anyone he could eliminate was, as he knew he'd be storming the guard positions. His mission was to cut the Woodbury numbers to better Daryl's odds of survival. Plus, the very second he got lucky & saw The Gov. He took & scored the kill shot, but Ben stepped in the way at the very moment
He couldn't just sit around & wait for the Governor to show up, the assault was time sensitive, using the walkers as a temporary diversion, so he could shoot down combatants & in the chaos go unnoticed for a short time
I thought it was actually pretty smartly done given it was a suicide mission, & it almost worked. Only a tenth of a second from eliminating the Gov.
Frankly, the Woodbury lot are a pretty poor unit. Rick's group has the edge there, & from the look of the finale teaser, they are either gone, or are in hiding & possibly plan to fight with guerrilla tactics, which given the state of their group, is as good a plan as they can muster. It is after all THEIR turf