The Tapir wrote:
Here's the perks and detriments of being a Lich:
Poison, cut, and fear immunity: The poison and cut immunities are nice since Sacrifice shields fare poorly against DoT effects. Fear immunity is eh.
50% disease and stun resistance: Disease resistance is nice for the DoT prevention mentioned above. Stun resistance is nice, but can be reduced by certain skills (albeit rarely) and also necessitates finding gear with stun resistance on it (again, not a huge deal, but still something to think about).
20% cold and darkness resistance: Irrelevant. Necromancers don't care about resistances with Sacrifice since any burst damage they'd meaningfully mitigate is already covered by Sacrifice, and resistances do very little for reducing small bits of damage.
No need to breathe: Nice, but this effect can be found on gear.
Infusions do not work: This is the main issue. Infusions offer so many benefits that Runes and Salves don't, and losing them means Liches are severly crippled in terms of mobility and defense. Heroism grants longer Sacrifice shields and allows necromancers to take up to double the hits while both are active. Movement infusions makes dangerous melee enemies a much smaller threat with their kiting potential and stun immunity. Regen infusions allow lower-leveled necros to keep dealing damage rather than focusing on healing while sacrifice is available. Healing infusions get rid of dangerous bleeds and poisons when wild infusions are on cooldown or would be blocked by other less threatening physical effects. Furthermore, most infusions are low-cooldown and instant cast, meaning they are available more frequently and are less likely to get blocked by stuns.
+6 Magic, Willpower and Cunning: Irrelevant by the time you get it. These boosts are minimal.
+3 life rating (not retroactive): Actively harmful for necromancers. Since Sacrifice only limits hits to a certain percentage of maximum life, having more life increases the amount of damage that can be dealt to you and, thus, requires you to be able to heal for more.
+15 spell and mental saves: Irrelevant. These will mean nothing thanks to scaling.
All resistance caps raised by 15%: See the cold and darkness resist section.
Celestial/Star Fury category (1.1) and 1.0 negative energy regeneration: Moonlight Ray is a decent damage low cooldown beam, which base necros lack. Shadow Blast is a mediocre AoE spell with bad range and a negligible DoT. Twilight Surge is only useful for regenerating negative energy due to the low damage and awful range. Starfall is an okay-ish damage blast with a stun which can be helpful occasionally. One major problem with this tree is that all of its spells will damage minions, meaning that it's only really useful for pure caster builds.
While the Insane winners are all using Lichform, it's likely due to a thematic choice rather than an actual pragmatic choice of "this will make my character better." The benefits that Lichform provides don't come close to making up for the massive detriment of not being able to use infusions that it brings with it, especially since the majority make no effective difference. Tinkers and salves don't do anything that infusions can't AND cost a category point, which requires dropping Light, Ice, or Shades, which are all crucial for a necro's damage output and healing. The only way I see Lichform being "better" than a base necromancer is if they're not using sacrifice so that the resistance boosts make a difference, but why would you play a necromancer without sacrifice?
If we are going to talk solely about viability here is how I see it
Non-Lich:
Categories: 1 Inscription slot, Shades, Advanced Necro, Second Inscription/Escort/Ice (pretty bad tree imo)
Inscriptions: Manasurge, Heroism, Movement, Shield/Regen/Healing
Could go tinker, but would have to replace at least one inscription for an injector (two is more optimal however)
Frees up at least 14 class points (1 undeath link, 5 Lichdom, 8 in Star Fury)
Infinite generics!
Less damage output and relies solely on mana bar
Sacrifice has better synergy with Heroism and more options to heal up
Less likely to be escort screwed
Lich as Tinker:
Categories: 1 Inscription slot, Shades, Tinker, Advanced Necro/Second Inscription/Escort
Inscriptions: Shield, 2 Injectors, Phase Door/Manasurge (not necessary with attachments)
Injectors have more versatility with healing, unstoppable, cleanses, etc and tinker provides item attachments
Far less class points
Less generics, but very manageable
Two great damaging spells (Moonlight Ray and Starfall) that rely on a second resource bar
Doesn't completely rely on Sacrifice due to res options
More likely to be escort screw (unless you scum save
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I also want to note that my guides are about learning everything about the class, not a step-by-step tutorial on how to build your character. My prodigies were Blighted Summoning and Eye of the Tiger. Hell, I even mention that if I played Necro again I'd build it differently. With that being said, I don't think Lich is a downgrade. Its at worst a slightly worse alternative to non-Lich and at best superior in many ways. Don't knock it until you try it out!
just because something can be done doesn't mean it's a good idea or that it helps anyone win. 
. I only make my guides based on NM just to guarantee I get to level 50 due to time constraints. Also, I'm not one to blindly accept "metagame" statements and I discourage them. I'm aware that Shalore and Ogre are the best races, Cauterize and Draconic Will are the best prodigies, Heroism and Movement are far better than any rune, crit power to boost damage late game, etc etc etc. However, I'd rather have players consider everything instead of just listening to others say they're worthless.