The classes available had to have some house rules to establish the flavor of the setting. One thing noted with each class is their armor bonus; this was done because there just aren't that many different armors available. Most warriors go into battle almost naked, but chain mail is just being developed. So I gave each class an armor bonus that equals the armor they are proficient in normally, and let them describe their armor themselves.
The campaign I ran had an infernal pact warlock (power granted by Crom Cruach), a druid (son of a bear spirit), a spot-on Slaine style barbarian, a viking fighter (who didn't scoff at heavy armor), and a ranger reskinned to fight unarmed like a monk. And a boar followed them around.
No Divine Classes—the celtic deities are natural forces that must be appeased through offerings and sacrifice; they are not benevolent higher powers
Fighter: Usually a noble born trained in heavy armor from a young age. Your combat challenge and combat superiority show your control in the midst of battle. The battlerage vigor build from Martial Power is a good option for this game.
--Light armor bonus +3 and Heavy armor bonus +7. Can increase heavy armor bonus to +8 with a feat.
Ranger: In many ways a typical Celtic warrior—fast and lightly armored. Since bows are not often used in battle, a ranger can take the Slinger Fighting Style. The beast master build from the Martial Power book is also very appropriate to this game.
--Slinger Fighting Style: When you wield a sling, the damage die increases one size (1d8 instead of 1d6). You also gain the Defensive Mobility feat.
--Light armor bonus +3.
Rogue: Warriors who use cunning, deception, and stealth are not considered dishonorable by the Celts. As long as your enemy is dead and you are alive, little else matters. Stealing is punishable by a fine, double if through stealth, but there is nothing inherently dishonorable about stealing, just as long as you’re not caught or can’t pay.
--Since shuriken aren’t available as weapons, rogues get a +1 bonus to attack rolls with slings.
--Light armor bonus +2. Can increase to +3 with a feat.
Warlock: Unlike druids who train for years, warlocks gain their power through pacts with a powerful being or force. The Fey Pact and the Dark Pact are especially appropriate to celtic warlocks, but any power can be interpreted easily to match the flavor of the setting. Warlocks and witches are often associated with the Morrigan.
--Light armor bonus +2. Can increase to +3 with a feat.
--May take a Pact Weapon Channeling feat to use ranged attacks as melee attacks through a weapon. This avoids opportunity attacks, and if using a named weapon allows you to use that weapon’s benefit on your warlock power.
Warlord: Warlords are usually nobles who encourage their tribesmen in battle. They fight wearing heavy armor. Inspiring warlords are the most common, constantly yelling taunts and encouragement in the thick of battle, but a tactical warlord who uses cunning is valued as well.
--Light armor bonus +3 and heavy armor bonus +6. Can increase heavy armor bonus to +7 or +8 with one or two feats.
Wizard: Wizards are the most mysterious branch of the druidic order, for they have devoted themselves to harnessing the magic of the world. They sometimes refer to the Earth Dragon, spiral energy, or “the serpent” when describing arcane magic. Wizards are masters of rituals, and know more ways to accomplish the impossible than anyone.
--Wizards can use a one ritual they know per day without paying the component cost. At paragon tier they can use two per day and at epic three per day.
--No light armor bonus. Can get a light armor bonus of +2 for a feat and increase to +3 with another.
Barbarian: These represent the ultimate Celtic warrior, a raging madman. More than just training, your rages are a gift from the earth goddess, allowing you to channel raw elemental energy through your body. Legends tell of warriors caught in riastrad (battle-frenzy, or more accurately, warp-spasm) who twist around in their skin, their bodies burning the air around them. Your rages manifest supernatural powers.
--Light armor bonus +3. Barbarians often wear as little armor as possible so they don’t ruin it with a warp-spasm.
--Barbarian powers do not require a two-handed weapon. They are also proficient with light shields.
Bard: Bards are no mere wandering minstrels. They are members of the druid order first and foremost, though their magic specializes in charms and deception. They are valued as news-bringers, announcers of heroes, and tellers of legends. Bards can also act as social equalizers, for they can spread the misdeeds of heroes and kings through song and satire.
--Light armor bonus +3 and heavy armor bonus +6. Can increase heavy armor bonus to +7 or +8 with one or two feats.
Druid: The druid order passes on the secrets of the universe through oral history, training its members for years. Any class with the proper training can become a member of the order, but folk commonly associate the druids with controlling the weather and changing shape. You are a natural force yourself, powerful like the storm and wild like an animal.
--Light armor bonus +3.
Warden: Though barbarians and fighters claim much of the battlefield glory, legends tell of one warrior who trained with the druids, learning some of their magic arts and becoming a great leader. A warden combines great strength with earth magic, using the power of the elements around him to augment his attacks. They also learn how to change shape, taking the form of animals and natural powers in combat.
--Light armor bonus +3.