There were a few inspired encounters in Rappan Athak, but mostly the adventures creativity was confined to using 3e's monster creation and modification rules (advancement, templates, class levels). As such, it's an excellent resource for the time it was created in how you can use 3e's rules to create truly unique and dangerous monsters, and it does expose a modern player to some old school design techniques but I'm not sure that it's an adventure that has really aged all that well. I feel it's an adventure for groups that really dig system mastery and I can't say that it's really feeding any other aesthetic of play. If the group is the sort that loves squeezing every possible +1 into an action, plans out characters and moves with excel spreadsheets, and charops to the point that they have some 'hammer' power that lets them treat all problems as a nail, then they'll probably do quite well and have a lot of fun. Less serious minded groups perhaps not so much.