Earthshaker is one of the best innitiators in the game. If you want to go pure team fight, and pure win, use this build.

Early game you tunnel vision your way to mana boots. Use them so you can harass with your first ability more often. Then blink dagger right after that. It turns ES into a very mobile initiator.

Pop in, hit your ult, then your first and second abilities and you've not only stun locked their team, but you've likely gotten a few kills. If not, your team will mop up. Rinse, wash, repeat, win.