Actually, though, I'm not too well-versed in the ways of Stone Soup. I've spent much more time with the original Crawl, which has a delicious DS port. The games are similar enough that this doesn't matter too terribly much, but naturally Stone Soup has a lot of features that Crawl lacks, notably, a few new gods and species. And speaking of species...
Crawl has a lot of them. Actually, the only new ones on that list are Deep Dwarf, Vampire, and Felid; Crawl had Ogre and Ogre-Mage as separate species, but you can see they've been rolled together for Stone Soup. (Probably a good thing -- are they really different species?)
Here's the quick rundown.
Humans are humans. Nothing special, no skill affinities, no experience modifier.
High elves and deep elves are elfy elves. Deep elves are weaker but more magic-affine.
Sludge elves are drow wannabes. They're good with unarmed combat, but not tough enough to make it a very good idea.
Mountain dwarves used to be split into mountain and hill. Since I can't tell you the difference between the two, combining them was another good move. These are dorfs to the core. Give them an axe and some heavy armor and they'll be happy.
Deep dwarves are a novelty class that doesn't regenerate. They do start with a wand of healing and the ability to recharge wands at the expense of a permanent point of MP.
Hill orcs are orcs, which play a lot like their mortal enemies, the dwarves. Of special note is orcs' patron deity, whom no one else can worship.
Merfolk are nonetheless very land-capable. They only go into fin mode when they're in water. Proficient with tridents and ice magic.
Halflings are the tiny fellers we all know and love. They're hard to keep alive.
Kobolds are a lot like halflings, but with somewhat better skill proficiencies. They are carnivores and less picky about what they eat than any other race.
Spriggans are tiny, speedy little things. They are quite a bit faster than the second-fastest race. They make good assassins.
Nagas are snake-people, naturally. They don't make a lot of noise as they slither, but they don't move as fast as other races, either.
Centaurs, on the other hand, are quick on their feet. They're great with bows and less great with things that aren't bows.
Ogres are big louts with the power to hit things really hard.
Trolls are a lot like ogres, except they regenerate quickly, starve quickly, and are dumb as rocks. Trolls are just as happy to claw things apart as to bash them with weapons too big for most races to wield.
Minotaurs' unusual anatomy precludes the use of most armor, but they're fairly intelligent for a large species and get extra attacks from their horns, even when they're using a weapon.
Kenku are bird-people. If you get one to survive long enough, they can flyyyyyyy. Note: Birds are not known for their exceptional hardiness.
Draconians start out only dragonlike in appearance, but as they level up, they take on a color and get abilities based on their color. You can't control what they grow into, so this is a crapshoot.
Demigods are an indistinct race of something combined with a god (in the great mythological tradition). They have great stats, but they level up extremely slowly and they can't worship a god, which sucks.
Demonspawn are regular humanoids with mostly bad skill modifiers, but once they level up a few times, they start to mutate and gain cool powers. Like draconians, the mutations are random and uncontrollable. The "good" gods won't accept demonspawn followers.
Mummies are exactly what they sound like. Being undead abominations, they neither eat nor drink -- which means they can't starve, but they can't use helpful potions. A gimmicky race that takes some optimization/trickery to perform well. Mummies are also excluded from certain racist gods.
Ghouls are shambling corpses who are in a perpetual state of rot. Little pieces of their bodies start to fall off unless they feed constantly. Ghouls are dumb, but make decent fighters. Those racist gods won't take ghouls, either.
Vampires exist in limbo between life and unlife. Feeding on blood makes them feel more human, while dieting makes them feel more dead. If they go without blood long enough, they'll stop regenerating; some players like to keep their vampires just above this line to keep those handy undead immunities. Racist gods etc.
Felids are cats. Not catmen, not catgirls, just cats. This places some severe restrictions on what they can use. No weapons and I think they can't use wands either. In exchange, they have nine lives, earned as you level up.
Crawl doesn't have "character classes" as such -- what you see above are referred to as "backgrounds." This is apt, since anyone can eventually develop any skill. Your background determines starting equipment and skills.
Warrior backgrounds are all about dealing physical damage, with or without weapons. Fighters are better-armored than gladiators, but gladiators have some throwing weapons.
Zealots start the game already worshipping a god. The healer god is one of those racist gods, so not all races qualify. The chaos knight background is in grey because it is not a recommended background (even for humans, who have all recommendable classes recommended).
Warrior-mages are watered-down warriors and watered-down mages, specializing in schools of magic that don't deal direct damage. They're generally pretty nice if you can get them to survive a couple of levels. Skald used to be called Crusader until just recently. I'm not sure why it changed.
Mages are exactly what they sound like. The wizard background is for people who can't pick a school. The conjurer background is for people who can't pick a school but know they want to blow things up.
Adventurers are do-it-all types; in other words, they do everything poorly. Artificers are new and I think they're Use Magic Device-types or something.
OKAY. Intro over. Who's our first victim gonna be?