From what we have gathered:
1st boss is simply dps until 40%. At that point it starts using a skill called Hate Mission or such. This skill gives him a buff that increases his damage for every stack. Easiest way to get around it is simply run away from the boss when he uses any cast skill and you take little damage. Not sure what the boxes are for yet. As for the cage, the person inside it can kill it with white hits (w/m - r/m - k/m etc op) or those from the outside can target it and break it similar to the bell on 3rd GCH. ~~ This boss can even be hard when you can burn it. Just serenstum once you see the boss casting Hate Mission and keep going, will have to dodge skills after that though if you hadnt downed it by then.
2nd boss is just strait dps really..as long as you drag the boss towards the entrance of the room away from all the adds that spawn, not only will the adds not hit many (if any) of your party but for some reason the boss's aoe cast skill hits less.
3rd boss is by far the best boss there (It has a strat!!!

), though still really easy. Simply tank it and every now and then 2 pillars will spawn with a mob in it, kill both the mobs and click on both the pillars and the 90% reduction will disapear for a short duration, at which time you'll have to repeat.
4th boss is really hard unless you burn. From what we have seen, if you get some tornado on you, move away from other players otherwise you get hit for a % damage for all those around you. After a certain time the boss goes immune and it'll use a skill similar to the 1st boss Bela (1 hits everyone). This can be avoided by using damage reduction skills (magic) or serenstum. (wait 3-4 seconds after he goes immune before using seren)
5th . . . lets just say if you can't burn it then I very much doubt you'll have got past even 1st.
6th is interesting. Spawns pillars and some orb thingos that more around the room randomly. They do % damage to any near them. Boss casts a skill that places a massive sword above the tank, and after 2 seconds it slams into the ground damaging those it hits. Seems a lot like a simple dodge adds (pillars) and keep dpsing boss.
7th we dont really know anything about. Except that after a certain time boxes much the same as those from AC drop down and cause the boss to use Spirit Bomb and wipe everyone. lol.
This is all observations from Hard Mode and may or may not be correct ^.^