Can someone pleasee xplain to me how Illusion magic works? I know that is a really broad question but I am just unclear about the details. I am mainly concerned that either A it just isnt very useful or B after enemies get to a certain level, even the highest tier spells cease to work.

It's useful for one thing only: when using sneak attacks, calm an enemy after the first attack and attack again if he didn't die.

It's best for squishy characters or trouble-makers.

I've only gone up the right side, but I assume if you get the middle perks your spells will affect all enemies except maybe dragons. I've never tested Invisibility on dragons because I'm trying to kill them before they kill NPCs but I've never been spotted by anything on which I've used it including Death Overlords and Dragon Priests.

With Kindred Mage and Hypnotic Gaze, Pacify will work on humans up to level 38. Dual-cast that for 220% power and yeah, it's SO WEAK.

In short:

1. Dual-casting even the basic illusion spells (Fury, Fear, Calm) with the middle and right branch perks can apply their effects well above level 50. So it should be a rather long time before they stop being useful (read: virtually never!) However, they're not useful against Dragons.

2. Fury spells are best cast at a distance, to open a fight; this gives the best chance to have enemies actually turn on each other. It doesn't work very well against wolves, since the wolf tends to charge you for about 15 meters before it kicks in.

3. Fear spells are useless - you'll lose track of the target.

4. Calm is great for getting out of combat or setting up "calm and cut" sneak attacks.

5. The Courage type spells are best used to power-level, since you can cast them on groups of town NPCs, usually safely. If you have a follower, or use summons, you can buff your allies but not yourself.

6. Muffle is good until you create (not just find) muffle enchant boots. Invisibility is prohibitively expensive and better gained through potions.

7. If you like using Dragon Shouts, Quiet Casting works on them. Throw Voice will still work as a scouting / distraction tactic, since the taunt isn't silenced.

In conclusion, Illusion encourages a creative, intelligent style of play that complements (but cannot quite replace) actual combat trees.

This is true so I enchant gear with Fortify Illusion because I have Extra Effect and I don't use Fortify Health, Stamina, or . Plus, you can put them on rings and necklaces to carry and equip as needed.

Cast fury on one enemy and wait until it attacks another enemy. Then cast fear on the one that was attacked. It'll scamper off with the attacker in tow and soon they'll both be long gone.

Not entirely, in a dungeon fear makes enemies bunch up at the end of a section for a perfect frenzy opportunity. Of course, it's most effective with Draugr so you need to have 90 skill to use it.

Fear spells are definitely not useless. Enemies will run in fear and refuse to fight back. You can freely kill them however you please as they run in fear, sometimes they even cower in a corner for you to kill them. AS for losing track of the target either use detect life/undead or aura whisper shout.

I'll certainly admit that my annoyance at things running away (and out of LOS of my archery, as best they can) skews my assessment of fear. ^^

That would really depend on a build wouldn't it?
The reason it is so expensive is because it is so powerful if you can figure out how to use it (many can't- for some reason). Potions are a sub sure, but you don't run out of mana and have to go pick it (alchemy) and you don't have to pause the game every single time you want to use it. (which may just make you start using it alot more than you thought you would).

LOL. It's fantastic for getting enemies to kill each other (Fury/Frenzy). Enrage a draugr deathlord, have him clear a room for you. Then kill him by whatever means you like. If you have the perks high enough in Conjuration, you can then raise a Dread Zombie from him and put him back to work.

I've never tried Dread Zombie, the description says 30 points for 60 sec; is that enough for a Deathlord? I thought they were higher level, or does 30 points mean something else? Sounds like fun though.

At level 70, where my mage is now, sometimes I can raise them, and sometimes not until after several tries. It's almost like a range or aim issue, but is so ambiguous that I just can't tell. One problem is that a failed raise kicks the body away, so if the body is on a bridge it may fall into some inaccessible location.

If you wish to "Use Your Illusion" (HA! how old am I?) to it's maximum potential, you must take the Silent Casting perk.