IMO it wasn't exactly a good race... (to be more exact: one that could "safely" be added in warcraft 4)
What a 5th race should have is originality while still staying coherent. Creeb rebellion was just dumping totally random creep in 1 race.
For example: stay to ONE theme. The human alliance is made of dwarfs, humans and blood elves. Basically their appearance is nearly the same. NE fit together too because every unit lives in a forest. Most of the units also share the purple skin color.
using a gnoll with a troll and a satyr with an ogre doesn't make a new "race" IMO...
To make a race good, you should stick to one theme (e.g. Burning Legion or Naga or perhaps extending one of the smaller races like trolls, Goblins, ...). If you pick e.g. Naga, you'll have to add some none-naga units to the race. Try to only pick models that live in water. If you create a Demon race, pick units from the Outland tileset such as draenei, shades, nether dragons, doom guards and perhaps even fel orcs.
Next you'll have to decide what will set your race apart from the other 4 and make it interesting to play. I don't just want to play "human" with a few other models and names. Just look at the differences between the existing races and exploit them. E.g. Decide what gathering system you'll chose: Mining, acolyte / ghoul harvesting, wisp harvesting, or perhaps combinations?
Another example is the construction type: Don't base a gnoll worker off a wisp or something cause gnolls don't dissipate when they create an ancient...
Perhaps you can think of a totally different Tiering system?
Just try to differ from the other 4 races as much as possible. I've played some maps featuring 12 races or more. Sorry, they're bad because they all play the same. A race should be balanced and - like Blizzard themselves said - fun to play.
I've made some theoretical races (as in: made them on paper, never found the time to make a decent map out of it). If you don't have ideas, feel free to use some of these, though I'd like to receive some conceptual credits if you litterally use them
Burning Legion;
Harvesting system: Same as undeath; Acolytes.
Construction system: Summon structures (undeath). No blight needed. Only a limited amount of structures including:
- Nexus (main building)
- Altar (heroes) ~Demon Gate
- Tower / Food resource (unlike any of the 4 races, the tower building provides 8 food. Compareable to undeath, but no upgrade is required!)
- Upgrade building (contains all upgrades for weapons & spells)
- Research building (contains researches that unlock unit types).
Typical to the burning legion is that they summon their army on the battlefield.
Acolytes have a second ability that opens a new "spellbook" containing various unit summons. Those summons cost resources, and you need to research (research building) some unit types first. When you summon a unit, a portal will appear on the battlefield and will be 'summoned'. Once the portal is finished, it'll be unsummoned and a new unit will appear.
Most Legionarry units are incredibly strong. It is said that some units like the Doom Guard can be as strong as a hero.
One large disadvantage is their incredible vulnerability for dispels. All units (except for heroes) are in fact permanent summons, which means they take damage from dispels. To make up for this weakness, they have an upgrade that reduces any magic damage by 50%.
The tiering system is odd too. Unlike any other race, the burning legion actually constructs a
second nexus to enter tier 2. This can be both an advantage as a disadvantage, since there are 4 tiers.
Wizards;
A secret guild of wizards has joined the battlefield of Azeroth.
Wizards use the normal tiering system.
Unlike the other races, this race has four mage-units that all have 3 (2 researchable) spells. They represent one of the four elements. The Watermage is adept at healing, wind mage is good at illusionist magics (invisibility, miror image, ...), the Earth and Fire mage are good at buffing and fighting.
4 heroes means 4 elements too.
The worker (an apprentice) can harvest, build structures and build Golems. Golems are very powerful beings with many HP's and armor, unlike their companions, the mages. However, Golems require mages in order to be build. a Water Golem will require at least 1 living watermage. To "heal" golems, they actually have to be repaired. The repairability is researchable for all mages.
The shopbuilding has an interesting additional ability: mana regeneration aura. Any nearby friendly unit will regenerate mana faster near this unit. Perhaps pro's will like to actually build one of these on the battlefield...
Just some random ideas...
