Firstly, the GM Screen is marvellous. The exterior artwork is just beautiful and really aids the GM in setting the mood and flavour of the game. There is plenty of inspiration just from these images. The data on the screen is highly relevant and usable, especially having the Honour table at a glance. Overall, it is a well-designed product that any GM would find useful.
On to the adventure, then. 'Descent into Darkness' weighs in at 20 pages, with 13 of those devoted to the module and the others for NPCs and the map. It supports its claims to be a 'plug-and-play', region non-specific module very well and the designers have done a good job of leaving enough blank areas for the GM to fill and customise it for their own campaign. IT is even open-ended enough that it could be used as the introduction to a much longer campaign arc.
After reading through the whole module, all I can say is 'wow'. This is an especially dark piece of work (for L5R) which is justifiable given the nature of the conundrum placed at the feet of the PCs. There is a huge emphasis on thinking before acting, socialising and investigation to uncover the true activity behind the module. When the PCs do figure it out, they are left with a horrifying choice. This should lead to a lot of really good roleplaying scenes and characters doing some soul-searching before they can reach a sense of closure.
The module is well laid-out, and there are scaling tips in some encounters to give some advice on not only making the encounters more challenging, but also dealing with evoking the adventure (the one entitled 'Not dark enough?' has some great tips).
I think that this could well be more than a night's play to complete, depending on how much characterisation and investigation the players want to undertake. In preparation, I would warn any GM to have a contingency plan (and this is dealt with in the module too) as there are some open scenes which can potentially change the entire gameplay. Whilst this is distinct possibility, it only detracts in a small way from the product.
I'm really looking forward to putting my group of players through this. As they are interested in L5R, but have a strong background in White Wolf games, this will be a perfect hook to get them into a campaign.