What we, by which I mean I, know:
- There are at least two types of dragon - Fire and Frost. The latter is more powerful.
- Dragons fly by means magickal. When they are sufficiently hurt, they can no longer fly.
- When in melee, dragons have a bite attack.
- Their M.O. is attacking then circling the Dovahkiin to repeat the attack.
- They will mess you up. Todd's 999 HP demo character lost a significant chunk of his health fighting a frost dragon.
- They will hover and land if the mood strikes.
When airborne, it seems that we have only a few offensive options. The first is archery. The second, ranged magic - whether through casting, staffs or scrolls. The third - ranged Dragon Shouts, such as Storm Call. The fourth, relying on allies - conjured, companion or convenience.
A few things occur immediately regarding the three options. In regards to archery - this is where alchemy may show its strength. We don't know if dragons can be poisoned, but if they can - powerful toxins delivered by bow could deal significant damage to the foe while it is still airborne. Some of the archery perks will prove useful. Unlike hapless bandits waiting to be picked off, dragons when attacking will be constantly on the move. Slowing time when zooming will allow for increased accuracy when facing them - wasting poisons could be a costly mistake.
On magic - particularly destruction, Fire Dragons would seem to have an inherent weakness to Frost. Given Frost magic's ability - slowing down opponents - this may allow the mage to outmanoeuvre and outgun the flying menace. It is unknown whether the dragon's flying ability is drawn from a magicka pool or innate shouts - I suspect the latter. If so, one shouldn't rely on Shock being too effective.
A few shouts have been revealed. Pretty much all of them can be used tactically against the dragons. The one demonstrated in the demo, STRUN BAH QO - Storm Call - showed its effectiveness. It seems to be most effective as a 'fire and forget', using it to deal damage while you take cover and restore your health. IIZ SLEN NUS - the Ice shout - may also be an effective ranged tactic against Fire Dragons. The first level spews ice crystals, the second freezes opponents. Likewise, YOL TOOR KREIN - the Fire breath - could be effective against Frost Dragons. The ones that aren't directly offensive still have their uses. When lining up a shot, TIID KLO UL - slow time - will buy you valuable second to lay into a temporarily helpless enemy.
The last option is getting someone else to fight for you. We already know of a ranged companion - the elf in Riverwood who has romantic troubles. Wise Conjuration users will summon ranged companions - in Oblivion, undead like ghosts and liches generally used ranged attacks. If you're lucky, guards nearby will help you out. Spell buffs for your allies might be called for, if available.
The business end of a dragon is the mouth - bites and breaths emanate here. It would be prudent to attack the dragon from its flank whenever possible. Since they do land, patience and a game of cat-and-mouse may be necessary if no ranged attacks are available.
Potions are always handy - another way alchemy proves its worth. Restore Heath is a good catch-all, Restore Magicka for mages and Restore Fatigue for warriors. If available, Resist potions could blunt the magickal attacks of the various dragon types.
So, how will you take down dragons? Have you formulated any tactics that may be effective when trying to gather the necessary souls?