Slimes and oozes have become iconic creatures in D&D, but I have some comments and suggestions about how they should be used, connected to ideas raised in the screwage post. These are certainly nasty creatures, and depending on how they are used, may be interpreted as unfair actions by the GM; they are hard to detect, immune to large bundles of attacks as written, have hidden special abilities, defenses and weaknesses determined basically by coloration, and should basically be avoided unless the party knows exactly how to deal with them.
First, some terminology: I want to separate them into two broad groups: slimes, which are basically passive infections, and oozes, which are active scavengers. I can only remember one slime, the green kind, but there may have been others, and certainly there's potential for modification. The original oozes were the ochre jelly, gray ooze, and black pudding, in increasing order of danger.
Slimes don't move, at least at combat scale; they might be able to seep across surfaces at a very slow rate, maybe 1-6 feet per hour. They're more of a trap than a monster. Oozes move towards food, can pass under doors or through cracks and small openings, devour living matter on contact, and basically behave as if they were a mindless swarm of tiny creatures acting as a group. The color of an ooze can make it hard to detect in some environments (gray ooze resembles wet stone.)
The differences between oozes are the hidden abilities I referred to earlier. There's no logic to the differences; they definitely appear to be intended to break PCs out of their normal attack/defense routines. There's nothing inherently wrong with that, but it can be played wrong. If a particular slime or ooze is considered pretty well known, then it counts as common knowledge within the game world and the GM should warn the players "you know that oozing creatures like this are hard to kill because of immunities".
It's also a bit unfair to have hard-to-kill "nuisance" creatures with no treasure if they attack and move as a typical creature. I'd argue that the original descriptions make it sound like the monsters don't so much attack as merely move towards and engulf. Given the slow movement rates of the oozes (black pudding is fastest at 6",) I'd say the intended response is to outrun the ooze or distract it with another food source. I think I'd change the ooze attack roll to an attack vs. AC 9, but with a defense bonus for the PC equal to movement rate + 1/3 Dex; it's all about keeping away from the creature until you can figure out its defenses and weaknesses.
Since oozes are mindless, there's an argument that distracting it with food should always work. Oozes move towards the closest non-threatening food source; I'd probably roll a d6 to determine how long it takes to consume a sizeable quantity of food.
As for figuring out ooze abilities, I think there should be clues other than color.
If it devours wood or corrodes metal, there should be appropriate examples near its lair: corroded or rotted weapons of previous victims, pitted wooden doors. If it is harmed by cold, its lair should be warm; if it is harmed by fire, it should slow its move as it approaches open flame, including a torch. I personally feel all the oozes should have the same basic defense against physical attacks: crushing and thrusting attacks have no effect, cutting/chopping attacks split the creature (with the gray ooze also taking damage, because this is its weakness.) Oozes should briefly recoil from attacks that do damage, to let the PCs know they're on the right track.
If slimes and oozes are fairly well known in the world, then they should be sorted by color or other visible qualities and assigned typical habitats. Characters familiar with those habitats should be specifically warned about the abilities, defenses and weaknesses of an ooze they are familiar with, when they encounter one. If, on the other hand, you want oozes to be mysterious until encountered, then I think it's fair to randomize the abilities.
I'd just have one creature, "Ooze", base 1 HD, AC 9, 1 die damage. Add more HD for larger masses; movement rate equals HD, up to maximum 6" rate, with movement up vertical surfaces equal to 1/3rd normal move, round down. 1 HD oozes are immune to crush/thrust attacks and are split by cut, chop, and lightning bolt attacks, but have no other special defenses. Each doubling of HD also adds one immunity (fire, cold, electricity, physical, acid.) Each tripling of HD adds one non-living material vulnerable to the creature's digestive juices (wood, leather, common metals, precious metals, stone, gem/crystal.)
Colors of oozes determine camouflage bonuses. Also, each color of ooze might be vulnerable to one ordinary substance, like salt, alcohol, water, flour, or wax; I'd leave the specific vulnerability open and give a 1 in 6 chance for each substance tried to be effective for that color. Once set for a color, all oozes of that color will have that vulnerability.
Also, for 2+ HD oozes, roll 2d6: if doubles are rolled and the total is <= HD, the ooze has an extra-special ability, like glue, projectile blobs, paralytic or incendiary excretions, or noxious fumes. If the total is > HD, the ooze has an additional weakness (damaged by light; double damage from cold, fire, etc.)