The only build that I would really consider running Earth Elemental in so far is an Earth Wizard build, and I probably wouldn't bring him out against a Forcemaster. That's what Iron Golems are for. If you're playing against a control deck, you're going to need to deal with control effects applied to him. On the other hand, he's immune to poison, so you can ignore those control options.
You'll need to use Force Push on your opponent and/or Teleport on the Earth Elemental or your opponent to get attacks through. Otherwise they'll just walk around it. An Earth Elemental is powerful enough that it's worth the effort to get attacks in with it. It's expensive enough that you need to be committed to getting a return on that investment, but it can be strong if properly utilized. An Earth Elemental is too expensive to leave to his own devices; it needs support.
The real advantage it has over Iron Golem is against stun/daze/slam. Iron Golems can be repeatedly stunned out, particularly with light and lighting attacks. Earth Elementals are much less susceptible.
The other consideration is if you need a zone attack for some reason. You can prevent swarms from converging on a square with an Earth Elemental, although I haven't played against a swarm strategy with my Earth Wizard, so it's hard to know how this would work out in practice.
