With the exception of level 6, each map has two or three 'states' it can appear in. Sometimes it's a minor change, and sometimes it can completely change how you navigate the level. For example, Frozen Tundra has a bridge at the top. It might be whole, or it might be broken, requiring you to venture all the way down into the pit to cross the level. But other than that, sort of? Each level has a set group of enemies that will appear on it; for example, level one always has lemurians, wisps, jellyfish, and robots, and the boss will always be Colossus, Wandering Vagrant, or Magma Worm.
As for other randomization, the teleporter spawns in a random location, although never nearby. Your character will also spawn each map in a random location, although I
think there might be only a few spawn points. I've never thought to remember them. Chests, shrines, and drone spawn in random places throughout each level, and sometimes one type might not spawn at all; I got a level 2 once that only had shrines. What item you get from chests and boss drops (and rarely elite enemy drops if you have the 56 Leaf Clover) are random.
As for the characters, you can basically group them into ranged and melee. The ranged characters are the Commando, Enforcer, Bandit, Huntress, Engineer, and Sniper. The melee are the HAN-D, Miner, Acrid, and Mercenary. Even then, they have different playstyles. Here's my opinion on each.
Commando: Commando fires quick, has a great move to pierce through all enemies, a nice evasion move (a forward roll that, if timed correctly, can even negate fall damage), and a suppression fire technique. His style is all about nimbleness and procing items. He's a fun and well-balanced character, but I've never been successful as him.
Enforcer: Enforcer is a bit of a tank. His shotgun has limited range but hits everything in front of it. He can shield bash enemies far away and throw stun grenades to immobilize groups. His evasion move has him plant his shield in the ground, making him completely immune to damage from one direction. I really want to like this guy, but I have no luck with him.
Bandit: Bandit is a sneaky killer. His fire rate is as fast as you can press the button, and he can hurl molotovs to weaken groups of enemies. His evasion is a smoke bomb that speeds his movement and makes him invisible for a few seconds. His fourth skill, Lights Out, is a high damage shot that, if it kills the enemy, resets the cooldown for his molotov, smoke bomb, and LO. I got my first victory as him.
Huntress: Huntress is a kiter. She's the only character that can move while firing her basic attack, and she'll auto-track the nearest enemy. Her Glaive attack throws a high damage projectile that ricochets off of up to three enemies, and her bomb arrow can deal a good amount of damage to a cluster. Her evasion move is a short range teleport that can be useful for a bit of extra distance on jumps. I'm not a huge fan, but I did manage to beat it as her.
Engineer: Kind of an area-denial character. His basic attack fires three rolling grenades that aren't very strong. His secondary lays a mine and he carries up to 15 that regen over time. He doesn't have an evasion; instead he fires four heatseeking missiles for pretty good damage. His fourth skill lets him place a turret or two to help him fight, but they have a slow (I think 45 second) regen. He's fun to mess around with but I don't take him seriously, even if I beat it with him once.
Sniper: The game describes him as a boss killer, and this is accurate, although at heavy expense. His basic attack is a powerful shot that requires a reload; this is done in the same style as Gears of War's Active Reload system, where you press the button at the right time to make your next shot more damaging. His secondary attack is aiming, which can greatly increase the power of the shot and let it pierce. His evasion is a long range back roll. His fourth skill scans a random enemy (defined as 'the toughest'); once scanned, all hits against that enemy are criticals. This guy sucks in solo play and I've never made it past level 2 with him, but he might be fun in multiplayer.
Next, the melee.
HAN-D: Slow and tanky as hell. His basic attack is a slow punch with good knockback. His second attack fires a drone, which hits an enemy and leeches health back; he can hold up to ten at a time, and acquires them by killing enemies. His evasion is actually an overclock; he moves and attacks faster, and his attacks have greater knockback and a stun chance, but it doesn't last long. His fourth skill is a slow smash with a hammer that deals great damage and launches everyone in a pretty good area around him. I dislike HAN-D, but I still beat the game as him.
Miner: The miner is all about dashing. His basic attack is a swing on each side with a pickaxe; it has little range, but it's fast and does pretty good damage. His secondary is a charged dash that can go through multiple enemies. His evasion is a backdash that deals damage and stuns. His fourth move sends him into the air (and can function as a double jump, if need be) and hits below him to damage groups. He's fun to play as if a bit weak and skill-heavy, and I beat it as him.
Acrid: The Acrid is the area-denial of the melee, plus status inflictions. His normal attack is a bite with good range that hits everything in front of him and inflicts poison. His secondary is a spit of some sort that also pierces and does decent damage. His evasion speeds him up and makes him leave an acid trail that deals constant damage and slows enemies; using this correctly is key to playing the Acrid and makes him a monster in solo play. His fourth move is an infectious spit that inflicts plague on the enemy it hits, and it can spread. I love the Acrid and have two wins as him.
Mercenary: The mercenary is the flashy guy of the game, as he moves like a ninja and carries a lightsaber. His basic attack is a swing that can hit three enemies in front of him (and I think it can hit behind him a few pixels, as long as he hits someone in front at the same time). His secondary is a whirling jump that hits twice and can be used as a weak double jump, but is mainly used to jump through crowds and hit people. His third move is a quick dash that inflicts damage; if it hits, he can do it again, up to three times before it needs to recharge. His final move has him disappear and inflict about six slashes on the nearest enemy, as long as that enemy is close. He's invincible during it. I haven't beaten it as him yet, but he's damn fun to play.
@ninja CE & anyone else wanting to play: My Steam account is same as here.