I like the theme of the deck, and the idea behind it. I worry about how you're actually going to hit your opponent, though. True, you do have some mana acceleration with the Dark Rituals, but you're only playing with 20 land. With all the 3, 4, and 5 drops you have, and considering the actual power of your creatures as compared to what your opponents will probably have, most games you're probably not going to have enough land. Remember that poison does not equal deathtouch, so your 1/1 creature for 3cc might not last that long... You're along the right lines including Phyrexian Splicer. You NEED more cards that make your poisonous creatures unhittable!
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It feels like there are WAAAAY to many cards you just have one copy of. Pick a strategy, then choose slivers which will help you achieve your goal. You need to decide how you're going to win: beatdown? control? In a Sliver deck, things like Lava Axe become very irrelevant. Remember that those cards take up room, and you'd rather play a Sliver, I'm guessing. If you want an idea of what I'm talking about, check out my profile. I have a Sliver deck there focused on beatdown which could give you some ideas!
I actually tried Sinew Sliver and Muscle Sliver in this deck at one point. The result I found after playtesting was that my opponents were much less prepared for the Winged and Crystalline Slivers. Those allowed me to both block more enemy creatures if I wanted or just build without worrying about the stray Lightning Bolt. Have you experienced differently with similar decks?