I see people going on about how illusion is this super-powerful school of magic, yet I just don't see it. Until you get to the point where can quiet cast, cast invisibility, and mayhem, there is nothing illusion can do that my own two feet can't.

Calm and Fear seem completely pointless. Oooh, I don't want him to hit me, so I'll spend a bunch of magicka to make him run away! I can achieve the same result without spending any magicka at all by having my char be the one that runs away. (And believe me, playing as a cloth mage, I spend a lot of time running away from enemies.) Plus, while I am running away my magicka is regenerating. Or I can cast a summon and run and hide behind it.

Until you get quiet cast, frenzy just lets the enemy know you are around. Sure, they might start fighting each other, but if they are close by, they are just as likely to take out their frenzy on you. Without invisibility, you now have a serious problem on your hands.

Another demerit is that if you miss your target, you are screwed. At least with destruction I have area effect spells. And with conjuration I don't have to aim at all.

I am finding illusion to be mostly worthless at low levels and once I get to the master level, makes them game rather boring. (Walk into a dungeon, cast Mayhem, clean up the left overs. Yawn.)

If the entire argument for illusion being so powerful rests on expert and master level spells, then I just don't see that it is all that great.

Its all about play-style and strategy.
Calm and fear are excellent for control, taking one enemy out of the fight when you have multiple enemies charging you can be life saving.

Frenzy is obviously a spell used from concealment, another good way to take an enemy out of the fight. One will always kill the other while the other will be weakened by the time you attack.

Illusion is about utility and control. If this makes you 'yawn' then dont use it. To each their own..

Yes, it does tell the enemies where you are, but 99 times out of 100, everyone attacks the person effected by the spell rather than you. This gives you a chance to become hidden again. Problem solved.

Just aim and do that and you're dandy.

Frenzy is only an Adept level spell but with perks can be utilized up to level 50 and beyond. Yes illusion can make it boring if you want it to. That's because it's so powerful. Can't understand how you don't put the two together.

Fear is useful for crowd control. Fear a couple of guys and fight the other one while they are running around. Calm can be used the same way or can be used to bypass enemies altogether if you desire. You can calm enemies that would normally be friendly if you want to role play a good guy who doesn't want to kill unless necessary. Frenzy is extremely powerful in that you can kill every enemy in an area except one without any real effort. If that's boring to you don't use it. But that doesn't change the fact that it is very powerful.

Most people talking about how powerful it is are talking about it as a whole not just low levels. Nothing is all that potent at low levels before you get the perks and the better spells.

Invisibility and Muffle speak for themselves. Quiet casting comes at 50 and that doesn't take long at all if you are using the spells a lot. Calm and fear are the two I use most at low levels. They are both great for crowd control and will hold enemies off for a fairly long time making them magicka efficient.

Personally I never use the Expert or master spells much at all. They just aren't needed. I find illusion to be a bit overpowered at times so I don't use it a lot but sometimes, when I just want to mess with enemies, it's fun to play around with.

As far as powerful goes I actually find Paralysis (Alteration) to be one of the most powerful spells in the game. It works on almost anything and even high level Draugr Lords can be paralyzed one handed. There are only a handful of enemies that are immune to the spell and certian enemies, such as vampires, who can resist the paralysis poison will fall prey to the spell. It's also fun to watch helpless enemies tumble down the sides of mountains, off of cliffs, or down stairs.

Use Illusion the right way and you can clear a whole dungeon without anyone ever knowing you're there.

I particuarly like using the Fury/Frenzy tier to turn bandits and other large groups against each other. Fun to watch. xD

Well, if I can pacify even Lord Harkon with illusion magic then It's far from useless.

Because you can imagine yourself as a Jedi waving your hand.