MAGIC
Dragons cannot use normal magic, as they lack hands - however upon reaching rank 10 in Dragon Form, they gain the ability to draw spell sigils in the air with their talons (or fins for serpents and wingtips for wyverns - hydra cannot cast spells at all). The five magic powers described above each unlock a sequence of crude attack spells based on the appropriate damage type, but in addition there are three specialised talents for dragon spellcasters:
Terrestrial Sigils: Allows you to draw spell sigils regardless of Dragon Form rank, and unlocks 6 non-offensive spells, as well as 1 offensive spell based on your Dragon Descendant talent. This talent can also be purchased by Dragon Hatchlings.
Celestial Sigils: Requires Terrestrial Sigils, and is only available to classed dragons. This talent unlocks 7 offensive spells (although you may already have 1 of these from Terrestrial Sigils), and enhances some of your existing spells.
Khaos Sigils: Requires Celestial Sigils, this represents the final level of dragon magic. This talent unlocks 3 powerful spells (one offensive, one defensive and one functional), and enhances some of your existing spells.
If you focus on creating a dragon spellcaster you should also invest in Elemental Spell Focus and perhaps Enhanced Deflection. If you've spare talent slots left over, have a read over the three Improved Spell talents as well.
DRAGONHIDE
Most dragons have a scaly hide, and can draw upon their natural abilities to lock their scales together for a temporary bonus - however they can enhance or exchange this bonus by selecting one of the three mutually exclusive hide talents:
Tough Hide: Doubles the resistance bonus of your tough dragonhide.
Thick Pelt: Replaces your scales with a coat of thick coarse fur, providing a defensive bonus in addition to the normal resistance.
Rigid Feathers: Replaces your scales with long rigid feathers, providing a huge defensive bonus instead of the normal resistance.
These talents are primarily for cosmetic purposes, but they can also work their way very nicely into both effective and thematic builds - for example Serpent Breed combined with Lord of the Seas and Rigid Feathers would allow you to create a wingless Feathered Serpent modelled after the Aztec god Quetzalcoatl, and the combination of talents would result in a very strong defensive build capable of extremely fast water-based movement.
These three talents can also get a strong boost from the Strong Magical Shields talent.
OTHER USEFUL TALENTS
There are of course many other talents that work well with dragon builds, but some are particularly useful:
Dragon Blooded, Iron Talons and Powerful Metabolism double the Dragon Form bonuses for your breath, talons and jaws respectively (something you'll really need to do if you want to use them as primary forms of attack). The Dragon Blooded talent also counts as 5 ranks of Dragon Form for the purposes of natural armour.
Natural Fortitude (requiring Toughness) can provide a solid boost to your natural armour.
Berserker Rage and Tireless Rage can give a big boost to your Draconic Rage.
Martial Gnosis (requiring Serenity, Mind Over Matter and at least one Style Mastery) is a very viable alternative to the powerful Draconic Rage.
Unarmed Mastery aids most of your attacks, but don't forget to take Whip Mastery for your tail.
Sure Footed and Evasion are normally weak choices for dragons because of their bulky scales, but are very effective when combined with Lord of the Seas or Dracolich Skeleton.
DRAGON GAME MECHANICS
Because each class in God Wars II has so many options, and they can often emulate each other to a certain degree, it can become difficult to really make an individual class stand out from the others. One of the ways I did this with dragons was to explicitly introduce some new game mechanics for them.
While the shapechanging powers of other classes are often interconnected (allowing players the possibility of using multiple forms in the same build), the three dragon forms (human, draconian and dragon) are both mutually exclusive and first-tier (i.e., they've no requirements, but are themselves required for several other powers) - thus the forms are more like three separate mini-classes with some shared powers. Furthermore, most of the shapechanging forms for other classes tend to require multiple powers - for example a vampire using Wolf Form will also rely on Claws of the Wolf for offence and Lupine Fortitude for protection. For dragons, however, all three options are bundled together into the Dragon Form power, which then relies on different talents to strengthen them to more potent levels.
Dragon Form does suffer from a lack of non-physical protection, however, which is where the five magic powers come in. These magic powers utilise a mechanic called 'scaling', whereby earlier ranks give larger bonuses than later ranks. For example the Fires of the Volcano power gives +10% heat armour and +5% heat immunity at rank 1, an extra +8%/+4% at rank 2, +6%/+3% at rank 3, +4%/+2% at rank 4, and +2%/+1% for every rank after that. This mechanic only applies to the dragon class powers, and encourages them to spread many of their ranks around, rather than focusing like most other classes.
Precious metals (and to a lesser degree gems) are heavily tied into many of the dragon colours and powers. For example a Metallic Pedigree dragon with Red Dragon Descendant will be a gold dragon. Red Dragon Descendant also doubles the bonuses of Fires of the Volcano, which in turn gives a damage bonus while raging. Wearing gold Dragon Barding also gives a direct bonus to damage, while adding gold items to your treasure hoard provides fuel for (and improves the scaling of) your damage buffs, as well as unlocking bonuses for heat attacks. The same is true for White Dragon Descendant/silver/cold/defence, or Blue Dragon Descendant/copper/lightning/speed - and so on. This provides a certain degree of consistency, and also encourages dragons to greedily hoard precious items, which I rather like from a flavour perspective.
Another important detail I wanted to take into account was the dragons' renowned affinity for magic. While most classes will either go pure magic or pure combat, I wanted dragons to always be at least passable in both - thus even a pure spellcaster dragon will have powerful talons and jaws, and even a pure combat dragon will have the ability to draw spell sigils if he wishes. I also factored this in to the breath weapons; every dragon has two breath attacks, one of which is classified as 'physical' and is based on their combat skills, the other of which is classified as 'magical' and is based on their magic skills. Dragons invariably favour one or the other depending on their build, but the option is always there for them to revert to the other should they wish to do so.
In an attempt to make the dragon form feel more like the dragons 'normal' shape, I made many of the commands that are normally human-only also work for dragons - for example a dragon can change their gender (and get the appropriate messages) while in Dragon Form, and also change their appearance via the 'appearance' command, selecting from various dragon-specific features. Although classed dragons automatically have the ability to shapechange between human and dragon form, I didn't want this option to be available for hatchlings - so I had to ensure that it was possible for a Dragon Hatchling to class as a full dragon without ever needing to be in human form. This required some reworking of the classing system (as the other classes are required to earn and wear a black sash from the dojo, while hatchlings cannot wear any equipment), but the result once again helped to differentiate dragons from the other classes.