Okay so I'm sure Diablo 3 leaves a bad taste in everyone's mouth, (and it certainly does in mine), but if Azmodan and Belial could make it in to this mod, why not my gal Johanna? D3 may have done many things wrong, but character design was not one of them, and I'd love to see the Median XL team's treatment of the Demon Hunter, Witch Doctor, Wizard, and Crusader.
Once I get more experience with the mod, I just might try writing up some fully fledged out concepts myself.
The Diablo 1 Warrior, Rogue, and Mage could also make fun additions, even if they're a little generic; finding a unique niche for them.
Here's, I guess, some potential base concepts for them.
Witch Doctor: Sustained AoE damage master. Many short lived minions, group poison attacks, and zoning abilities. Mediocre defenses and vitality, but can gain esoteric forms of survivability, such as lifesteal, and reducing enemy damage.
Demon Hunter: Ranged physical damage glass cannon. Can dual wield Demon Hunter crossbows. Hates being in melee against groups, but can learn several melee skills that focus on quickly dispatching single targets, including an "execution" skill that delivers instant death if the target is below a threshold. One skill path could allow Demon Hunter to be interpreted as "Demon who is also a Hunter"
Wizard: Sustained magical glass cannon. Less mana than most casters, plus high mana costs. However, their innate ability grants tremendous mana regeneration after not casting a spell for more than a second. (Also they get a fixed percentage bonus to feedback damage) They need to weave between mid-range and long-range quickly, kiting foes before blowing them up with stronger close range attacks.
Crusader: Nigh unkillable tank. Lowest offensive power, but can survive a beating, lockdown entire groups of enemies, and support a team. Would probably have a strong reliance on their mercenary in solo play. Like the Paladin, could go down a Dark path. Innate ability would cause a small shockwave when hitting foes in melee, dealing minor damage and applying a small damage and speed debuff. Shockwave would have increased size when using an area hit weapon, and would apply a minor physical resistance debuff when a mega hit weapon is triggered.
Monk: An oddball melee class. Can be a highly mobile, aggressive melee character. Can also be played with a good mix of damage and defense, but with far more mobility than most bruisers. But, the Monk can also shine as a support class, with healing abilities and team buffs. I would actually use Kharazim from Heroes of the Storm as a major source of inspiration; instead of supporting from the back lines, the Monk would have close-range support abilities they can perform while dancing through the front lines. As for builds unique to Median XL: A Shield Monk that gains increased benefits from a shield, but can sacrifice those bonuses for powerful shield-based attacks, Captain America style.
Got less ideas for the D1 classes, but I feel versatility should be where they shine
Warrior: A versatile spellsword: primarily a decent mix between offense and defense. They would primarily have utility based spells, but they can enchant their weapons for element based damage buffs: particularly important when fighting enemies with high physical resistances.
Rogue: A versatile ranged character. Could be built into a veritable sniper; able to take out enemies from great distances. Or could be built into a strong melee duelist, who makes up for low health with a high affinity for blocking and evading melee attacks.
Mage: A versatile spellcaster. Has a mix between offensive, defensive, and support-based spells. Also has a demon summoning build, which synergizes well with their support spells.