"The Standing Stone" is interesting because it can be played differently depending on how well your players can role-play and how you want them to play. If you and your players like straightforward hack-n-slash adventures, that's easy enough to create. Just have the PCs save the village and reap the rewards of a job well done. However, if your PCs like to solve mysteries, this module can be so much more fulfilling to play and figure out. Trying to find out who the real villain is can lead to some great role-playing on the part of the DM and the players.
As with the previous adventure in the series (the horrible aforementioned "Speaker for Dreams"), "The Standing Stone" uses scenes rather than keyed locations to determine the action in the adventure. However, this adventure seems to use them much more successfully as something more than a flow in which dungeons to go to next. Here there is a real reason to have the scenes -- they move the adventure logically from event to event.
As with the first two adventures in the series, this one does a great job of highlighting third edition rules. It gives DMs a sidebar to help them determine what to do when their PCs have a lot of divination spells that might unravel the mystery for them. It gives DMs examples of how NPCs would use their skills to foil the PCs attempts to solve the mystery. It does a nice job with monster templates and introduces some interesting villains. A neat little quirk is that they've tried to tie in this adventure with the first two in the series through small features. (At one point, an NPC has a blade with the mark of the dwarven smith that the second adventure in the series focused on.)
I'd certainly recommend that any DMs disappointed after buying "Speaker for Dreams" consider buying this adventure even if they hadn't planned to. In fact, I'd recommend this adventure to either DMs who like role-playing or hack-n-slashing, which is really nice.