I've been playing a Fire/Earth, recently hit 32, and have loved it the whole way up. Fire/ having a damage/slow aura and a quick-activating PBAoE hold/panic button seems to offer some great synergy with /Earth's heavy melee focus, and I'd imagine Ice/ would work well for similar reasons.
/Earth also offers a lot of soft control thanks to all its attacks having a very high chance for knockdown, so it'd probably go well with a more control-light set like Gravity/. For the same reason, regardless of what primary you pick, you want to avoid any immobilize powers that prevent knockdown. Since you'll be in melee a lot, immobilizing isn't going to do you a lot of good anyway, and you really don't want to negate all that great knockdown your attacks are doing.
As far as skippable powers, I've taken everything but Hurl Boulder. The definite focus in this set is on melee; Stone Spears isn't exactly the best bang for one's buck, but you have to take it regardless, and it's very cool looking, so your use of it really just depends on how willing you are to place style above substance. Tremor is a bit slow, but it's still a fairly nice power, and since it's your only AoE opportunity until 38, I'd at least start with it. You'll have to give me a couple weeks before I can say for sure if it's worth keeping with Fissure, or if the latter can serve as an effective replacement.
I haven't gotten to Mud Pots yet, but even though it was part of the reason I first thought of doing Fire/Earth, I don't particularly hear good things about it and its small range, so I'm currently planning to skip it, already having one damage/slow aura.
I'd like to make a new character and since im normally into brutes i think the smashy earth assault set is just right for me. I don't know what to pair it with tough, is mind/earth any good? also, would mind earth be a combo worth it to make permadom? And hows mud pots in the game? seems bad on paper, and what attacks are skippable in earth assault ( or the suggested primary).