When he’s still in dragon form, all you need from that room are some of his scales. They’re on the ground, if memory served; roughly two thirds along the way from the door to the altar on the other end of the room. You can spot them by the little glowing particle effect above them.
Just make mad dash for them, zigzagging all the way and pray he feels like missing you a lot. The actual ritual together with the book and blood can be preformed safely in the hallway.
After you’ve clipped his wings and he equipped his boom stick launching bow, the main problem is the aforementioned boom sticks. They hurt. A lot.
The best way I found to deal with him is to walk up to the bump in the bridge and get his attention with a single ranged attack if he’s unwilling to attack. He should open up with his explosive arrow, so when he fires that immediately jump backwards so that the bump in the bridge is between you and him. The explosive arrow should either fly over you or hit the bump, allowing you to quickly run up to him before he can launch another explosive arrow (expect to get hit with his regular arrows, but you can hopefully take a couple of those).
Once your close to him and start whacking on him, he should switch to melee. At that point you can simply abuse your superior agility and lure him to attack you with his sword, roll out of the way as he winds up his swing and immediately jump in to attack once, maybe twice, and roll out of the way again before he can recover from his swing. Rinse and repeat until he’s dead.
Also, do yourself a favor and abuse the quicksave. After you've done a fair bit of damage, run away to the door and save. Then go at it again.
Hope that helps.
Last edited by Raygereio; 01/01/11 09:09 PM.