Here are my thoughts on the skills and maybe how they could be improved in E6
Warrior:
Archery:
Bad skills: none
Skills that help other trees: none
Overall: If you want an archery character, you will want to maximize this tree. Well designed skills
Blocking:
Bad skills: Power/Deadly Bash (I just don't see the point of using your shield to do damage)
Skills that help other trees: none
Overall: Blocking is an effective mechanic that makes for a fun play style. Maybe a little weak in the beginning for deflecting damage. Not a great counter for someone who hides behind a shield in the late game, though.
Heavy Armor:
Bad skills: Skills aren't bad per se, just doesn't make sense in some cases (see below)
Skills that help other trees: Fists of Steel (I remember Bruce Lee wearing plate mail...), Cushioned (not sure how heavy armor is going to reduce falling damage)
Overall: Until you reach armor cap, heavy armor is a fun play style
One handed:
Bad skills: Axe skills, power attack skills
Skills that help other trees: none
Overall: I find that I don't put that many points into this tree, other than the 100% bonus to 1h damage. Plus, no skills for daggers?
Smithing:
Bad skills: Light armor side of the tree is a little weaker than it should be when it comes to weapons until dragon
Skills that help other trees: none
Overall: Skill is Over Powered and becomes a must for any melee character or armor user. I like that even low levels of this skill are useful.
2h weapons:
Bad skills: Power skill attacks imo, axe perks
Skills that help other trees: none
Overall: Would be nice to have a blocking perk, I don't tend to maximize this tree either when using 2h weapons
Mage:
In general - half cost for Novice/Apprentice/etc skills are often required, but I just don't like them. For example, the novice perk doesn't help at all for casting higher level spells, and you often stop using Novice spells when you are at higher levels. It would be better if the perk also gave a 10% reduction of magic costs for all spells in that school in addition to 50% off novice. Then it would be perks that you absolutely would want to have if specializing in that school.
Alteration:
Bad skills: none
Skills that help other trees: block/absorb magic damage (does spell duration affect things outside of alteration, not sure)
Overall: While I don't find myself casting alteration spells that often, it has some nice perks that would help anyone
Conjuration:
Bad skills: Dismissing summoned undead has level restrictions, so less effective at high levels (damage bonus would have been better)
Skills that help other trees: none
Overall: Useful skill tree with effective summoned creatures and bound weapons
Destruction:
Bad skills: none (rune perk is less likely to be used, but only a single perk)
Skills that help other trees: none
Overall: Perks are good, but destruction spells are underpowered
Enchanting:
Bad skills: none
Skills that help other trees: Enchanting is useful to all playstyles
Overall: Enchanting is very useful when maxed, however it is not very effective at low levels. 3% fire resistance is useless. It would be better if it was more like an armor rating. A low level enchant is very effective against a low level spell, but you would need a higher enchant to defend against a higher level attack
Illusion:
Bad skills: none
Skills that help other trees: quiet casting
Overall: Illusion is an interesting playstyle, however level caps make it less effective. It would be better if you just had it be less effective, not ineffective as you fight creatures higher than your level, so you need the perks to boost its effectiveness. Hard caps just make you not want to use the spells.
Restoration: