I think Minecraft should have obsidian armor. It could also have some special effects (e.g.A player is wearing obsidian armor so you need to have a diamond sword in order to kill him/her.) It would be really cool if this was in the game
Would this armor be a tier under diamond, but provide other benefits to make up for it not being as strong as diamond? If diamond weapons are required just to injure the wearer, then they'd be almost unstoppable to anyone without such weapons. I also want to point out that obsidian is actually really brittle. It would be like wearing razor sharp glass.
I do like the idea of armor providing benefits other than just protection though. I like the idea that the lower tier the armor (thus the lighter the armor material), the closer you can sneak up to enemies. This would make leather armor still have a use if you want to avoid fights, but still want some protection.