Check out Ethoslab on Youtube if you're interested in mobivators, but I don't recommend that style anymore. As slackathor said, mob behaviour has changed. I would recommend a piston and pressure plate system now if you're really into mob systems, or just find a spawner and build an efficient system around that.
Make sure you're a good distance away from the trap. Around 30-40 blocks. And yes, you must light up all surrounding caves. And depending on how big your four flat surfaces are, they may not be enough. Try adding more layers to your trap.
Tried and true method is using timed piston suffocation. Docm77 uses it in his cave spider grinder. It's basically where you hook up a sticky piston to a set of repeaters which damage mobs a certain amount. You will have to look for mob damage values and have some sort of experience with redstone.
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But I do agree with you on the beaches. And the swamps. They are hideous now.
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Diamond armour, no complaints. It is diamond armour.
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Redstone is now faster to mine, and the fortune enchantment works on it now.
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