I've played this game mode for several weeks now, an hour or 2 at a time and seen the game develop over time.

It's an extremely fun mode, especially to see your characters become over powered.
It's always fun trying to try reach the limit of characters potential.

A few positive notes to the developer.
1.The addition of expert mode, was a genius Idea, the fact that you get double the shards makes it way more fun to play, as well as re-roll the legendary shards.
2.The addition of 4m mode is great as well, for those willing to go through to hell of modifiers that are usually game breaking and much stronger enemies. Its a especially great if you want to really have a challenge.
3.The addition of multiple new heroes Is much appreciated, the more heroes the more fun it is to experiment with them.
4.The biggest drive for me and most of my friends to keep playing the game is the consistent content updates, and as I mentioned previously the ability to try push characters to their limits and test them at the final boss.
5.Lastly keep up the great work! It's a great game mode :)


Now a few critiques about the few last changes.
1.Recently there have been added a lot of new enemy modifiers which is cool and all, but in the same time they tend to be fairy annoying most of the time.
There is to many global effect modifiers that stun lock the characters, it makes it challenging but most of the time when you die because of them you blame that they are extremely unbalanced and not because of lack of skill. Here's a few examples of rooms I've come across which are extremely broken:
a) The primal beast, having Chaos Knights reality rift ability. Unless you can kill him
within a minute its all over, he charges toward someone and mid charge teleports you to him
and one shots you, It doesn't feel like its an issue with skill but sure I could buy linken's
sphere every game just to try deal with it? It works but its a waste of an item slot which could
be used to get a much cooler item. not to mention that the blink modifier operates the
same way, and that linken's sphere won't do anything here.
b) There is a broken setup of modifiers that that can kill a run with ease, specially if the
rooms have multiple captains. for example. a combination of the following : Bane's
Nightmare sleep ability, Razor's Plasma field ability (I know its from the original
labyrinth) and lastly,
Lion's Earth spike. these 3 in a room with a lot of captain creeps running after you as in
my case it was the slimes room (Not the slime boss) you kill a slime, get instant
nightmared, while nightmared a earth spike hits you dealing damage, and
lastly get hit by the Plasma field.
There is nothing related to skill in such a combination, the only solution is yet again, linken's
sphere or BKB and even those won't save you, linken sphere is a single use every 8
seconds? (including cooldowns) and bkb has a long cooldown. when its off cooldown, you'll
get stun locked again.
It's a near guarantee end to the entire run.

It's just the most memorable cases which infuriated me and many others for certain.
It's cool to have more modifiers but I don't think they should be stun locking the players.
not to mention being a melee hero against Earth spike is a guaranteed stun once you kill a captain as well.
I think the concept of the modifiers needs to be changed slightly from what they are now,
reduce the amount of stun locking modifiers, especially the instant ones.
and instead implement ones that don't stop the player from being able to play.
for example a great modifier that was implemented that I somewhat think is reasonable is the
Crippling fear It makes the game harder, however you can run away from it when it occurs.the radius is a bit ridiculous as it is today but things similar to that, another one I think would be best to add as modifiers are passives to creeps, for example: Mana burn on attack, Slow on attack, creeps have increased attack speed or damage when bundled up, temporary damage reduction to the player who killed the creep(Minor that stacks temporarily) Essentially it would be healthier for the game to make the creeps themselves be scary because of the modifiers and not the modifiers themselves. There is a massive amount of things that could be added to make creeps way harder to deal with. here's a list of potential modifier ideas:

• Mana burn on attack for creeps, reduce the players mana each time their hit.
  
• Movement reduction on attack, reduce the player movement each hit.
  
• Increase creeps armor, significantly possibility even 2 of this one so that creeps can be even much harder to deal with for physical damage dealing heroes. 2 is to create a degree of difficulty, if you're unlucky enough and get 2 modifiers for creep armor increase, make it so that physical damage is probably 80%? weaker against them? aka because of armor or possibly even more.
  
• Increase magic resistance, same as the above.
  
• Increase general creep damage resistance.
  
• Increase creep movement speed.
  
• Critical strike on creeps?
  
• Increase creep HP by a %.
  
• Tomb on death, was a great modifier in my opinion. (Already ingame)
  
• Abbadon's passive E Curse of avernus just without the slow effect, cause silence if
  a player is hit enough times.
  
• Anti mage's E Counter spell (Already game)
  
• Axe E? Counter Helix When attacked creeps have a slight chance to proc counter helix.
  
• On creep death, reduce player outgoing damage by 3%? for 10 seconds, stacking.(This would require balancing.)
  
• Captains have beast master's passive Inner Beast which grants nearby allied creeps bonus attack speed.
  
• Evasion on creeps.
  
• Reduced damage received from front.
  
• Reduced damage received from back.
  
• Burn aura around captain creeps, similar to radiance that does hp % damage.
  
• Elder titans passive E Natural order reduce nearby players armor and magic resistance by a significant amount. forcing characters with a lot of inbuilt armor (ie slark) to not be with 80 armor just from stacks.
  
• Enchantress passive R Untouchable for captains , reduce attack speed of players.
  
• Huskars W Burning spear creeps on attack create a fire debuff on player which causes damage every second, stacks.
  
• Captains have damage increase aura for creeps
  
• Captains have generally auras that make nearby allies stronger.
  
• Medusas Mana shield , creeps already have usually a manapool, might as well use it. especially bosses.
  
• Monkey kings Jingu Mastery on captains.
  
• Ogre magi E Bloodlust would be generally cool.
  
• Troll warlords passive fervor creeps gain attack speed on each hit on same target

I'm sure there's many more that can be done, I just gave a small list.

Closing remarks.
Players that play usually want to feel powerful, with each room that passes it's more fun to see the heights that the heroes can reach, so please keep that in mind when implementing new abilities. a lot of abilities like PA's queen killer, increases crit damage by 0.5% per crit done are great, same with axe's bonus HP and so on, would be great to add more of those to most abilities to make it so that every hero can become extremely powerful.
and try reducing the amount of the existing modifiers that hard punish players for simply playing, like the nightmare sleep. it just happens and nobody likes being stunned for no good skill based reason, if a boss stuns you because of his ability its your fault for not playing good enough, but if you kill a captain and get stunned for it? that's essentially punishing for doing what you're supposed to do.
and lastly please reduce the crippling fear aura on captains the radius is ridiculous, and is very annoying.

Aside from that the game mode is extremely fun and will keep on playing as it evolves.