I have only ever used Illusion in conjunction with sneaking, wondering how it plays without going the stealth route?

I always found it much too powerful when used with sneaking, made the game way too easy. When I play a pure mage I usually don't use illusion either, so maybe they aren't PURE mages.

Anyway, how does illusion differ when used with sneak or without it?

You don't need any sneak if you use pacify. Walk in the room. Pacify everybody. If you succeed without running out of magicka, game over. Your magicka regenerates instantly once everybody is pacified. You can kill them off one by one after that. 60 second duration is incredibly long, too.

It can work. But if you want to use fury etc you'll want to sneak into place and hopefully silent cast it.

Its great with magic using classes from what I hear. It potentially gives you a few extra minions or stops attacking enemies before they reach you.

Yeah fury with a non-sneak character is not a good idea, unless you're furying animals so you can soul trap them. Pacify is the way to go, because it removes enemy aggression, I'm not a big fan of fear because I don't feel like chasing after things.

It might give a reason to use calm or fear? I've never used fear and almost never calm. The one occasion I can recall calming was a troll that I took on so early one sneak attack wasn't actually enough to kill it. I calmed it, ducked back into hiding out of combat, and nailed it again, killing it. Once you get the dagger times fifteen perk, most successful sneak attacks are instant kills, even on master. I also once used the harmony scroll in the final room by the lift from Aftland and the stairs down to Blackreach. The two surviving members of the party are there and get into a fight. You can stand back and take out the winner, but I was curious to know if I calmed them both if I could then talk to them for some interesting new dialogue. Sadly no. They just stood there, no dialogue box, saying typical spoken lines until the effect wore off. Then they attacked me.

I loved command humanoid and command creature better, though they function in much the same regard for my purpose as fury. In Oblivion, the command effect, even when it wore off, would still have the victim being attacked by others. It's like the moment they see their companion as an enemy and he turns on them, they continue to want to kill him in retribution. This made an evil little two or three second command bow handy. Shoot a victim from the shadows, then stand back and watch the fun. But it would've worked (and on occasion when I messed up did) even if they seen you, provided a former "ally" was closer to them than you when you shot.

Another non sneaking thing I did in Oblivion that I miss in Skyrim was the combined use of charm spells to raise disposition and calm to lower aggression of an enemy. In Oblivion, enemies only attacked if their disposition was five points or more lower than aggression. Most creatures and NPC's in the wild had automatically severely low dispositions to ensure they attacked on sight. Make the charm effect just barely enough to beat that, and sometimes if your Speechcraft wasn't high enough, boost it, and the speech wheel could have turns on it. That meant you could play the mini-game, raise their natural disposition, and with perhaps a couple repeats, you could raise a monster or NPC's disposition permanently higher than their aggression and they wouldn't attack you even after spell effects wore off. You could even raise it up to 100 and they would defend you as a friend!

and silents your magic so that you dont get detected while sneaking