I am relatively new to magic but I like this deck a lot, It seems to have a lot of synergy. There are a few small objections that I have, however.
The first is one that I can't offer any suggestions for, unfortunately, and that is the fact that Strangleroot Geist costs 2 green mana to play. I also play a green/black Golgari deck with a zombie theme, and I often will draw a Geist in my opening hand, but not two forests. This could slow the deck down a lot. In my case, however, I am running guild gates and only 1 duel-colour land (since that's what I happen to own), so I have less chance of getting that all-important 2 green mana on turn 2.
It also doesn't synchronise incredibly well with the black-mana 1-drops you have. If you want to play a swamp to get a Crawler or Ghoul out, you can't get the Geist out on turn 2. You are basically relying on drawing a duel-colour land. Unfortunately, like I said, I don't have any suggestions on how to improve this.
Secondly, I don't like the amount of destruction you have that targets creatures. I would consider siding out the Murders for some enchantment destruction, perhaps in the form of the Golgari Charm. It can be used to destroy enchantments, but the other effects are very useful as well. You can give regeneration to all your creatures, or give all creatures -1/-1 until the end of the turn, which is great against tokens/triggering undying/taking less damage from attackers. Even if the opponent isn't using enchantments, you still have the other utility.
Last, I would love to see something to sacrifice the Crawlers to when they are out on the field. The fact that you have no method of drawing cards in this deck means you will inevitably have and empty hand. Therefore, in order to spend your mana in the mid/late-game, you might consider adding a Bloodthrone Vampire . Therefore you can repeatedly sacrifice your Crawler to the vampire before playing it again from the GY for 1 mana. Every black mana you have spare is a +2/+2 until end of turn for your vampire.