The writing team behind this adventure has released an update that addresses many of my reservations about it. It still has layout issues which detract from readability, which means I can't quite give it a full 5 stars (next time, guys, make sure your text flows nicely and just, well, LOOKS nice before you fill the page with art).

There’s a lot to like in this adventure. It’s your bog-standard "out and down" dungeon crawl, which some folks might yawn over, but there's a really cool premise I found quite interesting, and there's plenty in the adventure to keep your players on their toes. It manages to cover two of the pillars of play very well. Slayers will have plenty to kill. Explorers will find plenty of areas in which to poke and prod. Roleplayers won't find as much joy, but that's the nature of an out-and-down dungeon crawl, so I can't fault the writing team for that.

The dungeon itself is as dangerous as many I've seen. It's not as lethal as Tomb of Horrors, but Tomb of Horrors isn't really a good dungeon. There are too many ways to just die in ToH, with player choices and character competency having no meaning. The Dreaded Tunnels, like all good dungeons, is accommodating of player agency. If a PC dies in The Dreaded Tunnels, it's their own damn fault. There are plenty of ways for PCs to get dead in this adventure, but they're all due to choices players make (and die rolls, of course). I stand firmly behind that. 

There are new and interesting monsters, plenty of loot, new and unique magic, and compelling NPCs.

Much of the art appears to be custom-sourced, and it's executed to a very high standard. 

The map is an excellent, high-resolution PNG that can easily be slotted into your favorite VTT. The adventure also comes with a custom token pack for your VTT game, which is a pleasant surprise.

The layout is fairly well-executed. The text is laid out in a serif font, which I prefer, and I found it clear and easy to read. There are some problems with the fully-justified layout, like last lines of paragraphs spread across the entire line. These are pretty damning errors for a product which credits a graphic designer and layout artist, and could use a fix in an update.

The text is where my trouble with this adventure begins. For all the pretty, for all the maps and tokens, for all the ingenuity of the premise, it's just...well, there's no easy way to put this, so I'm just going to say it: It's just poorly written.

There are grammatical errors, there's shotgun punctuation, there's apparently random capitalization. Those are objective fact. There's way too much flavor text, which I admit is entirely subjective.

That's one thing. I can get beyond that to a certain extent, especially if the premise of the work is good, like it is here. But the writing in this adventure is so bad it gets in the way. It especially gets in the way of easily DMing the adventure.

5e mechanical text looks a certain way. Take a poison needle trap, for instance. Here's the Tier 1 example from my favorite online SRD:

A poisoned needle is hidden within a treasure chest's lock. Opening the chest without the proper key causes the needle to spring out, delivering a dose of poison. 

When the trap is triggered, the needle extends 3 inches straight out from the lock. A creature within range takes 1 piercing damage and 11 (2d10) poison damage, and must succeed on a DC 15 Constitution saving throw or be poisoned for 1 hour. 

A successful DC 20 Intelligence (Investigation) check allows a character to deduce the trap's presence from alterations made to the lock to accommodate the needle. A successful DC 15 Dexterity check using thieves' tools disarms the trap, removing the needle from the lock. Unsuccessfully attempting to pick the lock triggers the trap.

Here's how the writers of The Dreaded Tunnels did it:

The chest is trapped with a poisoned needle, requiring a DC 14 Investigation check for the players to spot it. Once identified, DC 14 Sleight of hand check to disarm. If unsuccessful, when opened, the target takes 1d4 poison damage. The lock requires a DC 12 thieves tools check to unlock, or DC 15 Strength to break it with a crowbar or similar tool.

It's like the writers never really took on board how 5e mechanical text is supposed to flow. It's like they've never designed a 5e adventure. Hell, it's like they've never read a 5e adventure, because mechanical description is uniform throughout Wizards publications, including AL adventures.

The DCs are wrong for Tier 2 characters, which is the stated design tier. It doesn't take too strict an eye to notice these checks are too easy for Tier 1 characters. Some of the checks are wrong. All of the skill checks in this example either fail to list the relevant ability or, if it includes the ability, fails to tell you what to do with the ability. In other words, the text includes none of the adjudicating shorthand official Wizards 5e (and quality 3rd-party) adventure material has made you come to expect. 

This is not an isolated incident. This is the standard throughout the adventure.

Elsewhere, there are mechanical things mixed in with the flavor text, like this:

If you decide to go on your left, you notice that the room is filled with nothing else than an unbearable stench that makes your insides turn. Make a constitution saving throw (DC 12) against puking. At the end of the room you finally notice what generates this horrendous smell.

This is supposed to be a room description. Reciting a player choice which should have been established before beginning to read, then giving the room description, then calling for a saving throw (formatted incorrectly), then removing player agency by assuming the PCs went further into the room, in the process contradicting the first bit of room description, is just...wow.

Again, this is not an isolated incident.

SUMMARY

Practically speaking, if you're an experienced 5e DM, you're going to need to really dig in to the 2 out of 5 text to ensure you know precisely what the designers are trying to achieve. Spending the time to do that will likely mean that running this adventure will take more time to prep than simply designing your own adventure (and needing to spend any time at all to prep a canned adventure other than read it once or twice means 1 out of 5 convenience) . But if you're prepared to do that, you'll get a cracking 5 out of 5 concept. Additionally, if you play online with a VTT, you get a lot of 5 out of 5 assets. 

I can't in good conscience give more than 3 out of 5 stars for this adventure. Submitted to a thorough editing and a top-down rewrite can bring it to 4 or 5. If that happens, I'll revise this review or add a comment to it.

You can find a clean copy of this review on my blog at www.r-p-davis.com