Well I'm now about level 18, a master of Conjuration, and an expert of Illusion. I've also finished the Theive's Guild. Combat for me is pretty much like this: Run around with Grey Cowl of Nocturnal on, see enemy from 120ft with life detection, summon a lich for 40 seconds on self, cast invisiblity on self, walk towards enemy. My lich then follows me and blows the crap out of any enemy nearby.

My only complaint is that the AI for summoned creatures isn't really good. My lich likes to walk around and do his own thing sometimes, he casts disintegrate weapon/armour spells on monsters when they do nothing to them (or uses fire spells against flame atronachs), he fires off huge spells that damage within ~10ft, but only when I'm standing near the enemy. I can summon deadroths too but they waste the first 5 seconds after you summon them casting buff spells on themselves, and then when they start fighting they miss with melee attacks a lot. I've summoned them before and they only hit the enemy once in 30 seconds. They only seems to be effective if you can get the enemy pinned in a corner so they can't get away from the deadroth. So far the most effective summon I've found for melee combat is the clanfear. They're super fast and they like to pounce on the enemy, which rarley misses and does tons of damage.

Maybe there will be a mod or patch or something that makes the summoned creatures smarter. At least make it so my deadroth only swings at the foe when he is actually close enough to hit it.