The values below are for the hardest difficulty setting.  In particular, enemies on the easiest setting have fewer movement points, while on the hardest setting they do more damage and are worth much less experience.

The actual experience awarded depends on the difficulty level and the experience of the soldier.  For example, killing a Ray'Ther on the easiest difficulty level could be worth 4 experience points for a new soldier but only 1 point for an experienced soldier.  On the hardest difficulty, a Ray'Ther is never worth more than one point.  Of course, on the harder difficulties there are many more enemies.

For each enemy, values are shown for action points, attack (range, accuracy, AP cost), attack damage, hit points, armor, and maximum experience seen awarded on the hardest difficulty level.  Next to the damage rating are a range of actual values seen, though these can be hard to judge because armor reduces damage, but some hits seem to bypass armor (or perhaps are double-damage "critical hits"?).

Most of the stats come from http://scayra.free.fr/incubation/.

The manual and in-game screens (and voice acting) seem to disagree on whether the names should be "Coo" or "Goo".  The naming is generally such that units whose names end with "Coo" have a ranged attack, while those ending with "Ther" must close to melee range; the Al'Coo is a notable exception.

Ray'Ther AP: 6 Rng: 1 (1AP) Dam: 2 (1-4) HP: 2 Armor: 0/0 Exp: 1
Weak melee-only unit, but fast, and often appears in large numbers.
Ray'Coo AP: 4 Rng: 20 (5%, 2AP) Dam: 4 (6+) HP: 6 Armor: 1/0 Exp: 3
Common ranged unit.  Can jump over walls, though doing so ends its turn.
Gore'Ther AP: 2 Rng: 1 (1AP) Dam: 20 HP: 4 Armor: 100/0 Exp: 2
Slow-moving, but heavy front armor means it can only be killed from behind (unless you have the Enhanced Laser Gun).
Cy'Coo AP: 3 Rng: 20 (3AP) Dam: 8 (4-10+) HP: 4 Armor: 100/100 Exp: 2
Immobile medium-range artillery.  Armor goes to zero when firing, which means it can be killed by units in defense mode.  It has slow targeting, always aiming at where a soldier was standing at the end of its previous turn.
Squee'Coo AP: 5 Rng: 20 (5%, 2AP) Dam: 4 (4-7) HP: 10 Armor: 2/2 Exp: 2
Ranged unit, similar to the Ray'Coo, but tougher.  When injured sufficiently, turns into a Squee'Ther.  You only get the full experience value if you hit it hard enough to kill it without it changing form.
Squee'Ther AP: 5 Rng: 1 (1AP) Dam: 2 (1-6) HP: 4 Armor: 3/1 Exp: 1
An injured Squee'Coo, capable of melee attacks only.  The front armor can make this annoying to kill with light weapons.
Al'Coo AP: 6 Rng: 1 (1AP) Dam: 20 HP: 100 Armor: 5/5 Exp: 7
Melee-only mini-boss.  Large unit (double height, 3x3 base).
Ee'Ther AP: 5 Rng: 1 (1AP) Dam: 2 HP: 20 Armor: 3/3 Exp: 2
A nearly-invisible melee unit with regeneration.  All damage heals at the start of its turn, which means you can soften it up with defensive fire.
Nor'Cyn AP: 3 Rng: 20 (10%, 3AP) Dam: 8 HP: 15 Armor: 7/255 Exp: 3
Mini-boss.  Large spider with laying tubes that fire in a similar fashion to Cy'Coo.  The above stats are for the tubes; the body cannot be damaged.  Lays Dec'Ther each turn.
Dec'Ther AP: 7 Rng: 1 (1AP) Dam: 50 HP: 1 Armor: 0/0 Exp: 1
Very fast acid-spewing spider unit.  They attack by exploding, damaging all nearby units.
Pyr'Coo AP: 5 Rng: 10 (5%, 3AP) Dam: 6 (5-7) HP: 6 Armor: 5/3 Exp: 1
Tough ranged unit.  Weapon has a 3x3 area of effect.
War'Coo AP: 3 Rng: 10 (5%, 3AP) Dam: 6 HP: 2 Armor: 100/100 Exp: -
Immobile short-range artillery.  Indestructible.
Tr'Yn AP: 10 Rng: 1 (8AP) Dam: 40 HP: 200 Armor: 9/1 Exp: 3
Boss.  Large unit (double height, 3x3 base).  Lays 3 Dec'Ther each turn.  Best hit from behind.  If it has to take more than two steps it can't attack, but the spiders it lays get to move immediately.
Gore'Coo [expansion] AP: 6 Rng: 40 (6%, 2AP) Dam: 4 HP: 14 Armor: 4/2 Exp: 2
Very tough ranged unit.  Can open doors and go into defense mode.
Tea'Ther [expansion] AP: 8 Rng: 1 (8AP) Dam: 40 HP: 30 Armor: 3/1 Exp: 2
Very fast melee unit.  Can't move and attack in the same round.
Bea'Ther [expansion] AP: 6 Rng: - Dam: - HP: 20 Armor: 3/3 Exp: 1
These don't attack, but they will cluster around you, impeding movement.
Bea'Coo [expansion] AP: 4 Rng: 2-4 (1AP) Dam: 10 HP: 12 Armor: 2/2 Exp: 1
Essentially a Flame Thrower with unlimited ammo.  Can fire 4x per turn.  When they die, they explode, causing massive damage to all adjacent squares.

If you're not sure what you're facing, click on the magnifying class icon on right right side of the game screen, then click on the Scay'Ger unit.  It will provide the unit's name and some trivial information about it.