This is a very solid, straightforward dungeon crawl, excellent for an evening of kicking in doors and killing monsters. The environments are very well thought out—the cave is convincing as an actual functioning den, with creative but plausible traps and setpieces spread throughout. The encounters are well balanced for a starting party, though if running at 3rd level I would suggest adding additional kobolds to increase the challenge. The hooks given to get the party into the adventure cover a broad range of potential motivations, allowing the GM to easily adapt this to any low-level party that finds themselves exploring the Underdark.

The writing is clear and easy to follow, matched by a simple and clean layout with beautiful art that's well suited to the atmosphere.

I do have some nitpicks with the way certain information is presented to the DM, though they're minor and very easy to work around. One environment hazard that appears in the DMG isn't given a page number callout the first time it appears (though the reference does appear later), and there's an important piece of set dressing (Faerzress) that doesn't offer enough information for a DM to give a physical description of it without having also read other material on the Underdark.

Overall though, this is an excellent adventure that I highly recommend for DMs looking to kick off an Underdark campaign.