Overall Dark Dungeons is a solid retro clone of the Rules Cyclopedia, although it's not 100% perfect (as with most retro clones). The author chose to incorporate a few of the optional rules in the RC and made them "canon", such as removing level caps for demihumans and allowing them to attain any level desired. The only offset to this is that a demihuman requires more XP to level up than a human. In all honesty this isn't that big of a deal breaker because let's be real, who used the level caps back in the day? Get Dark Dungeons if you want to play Rules Cyclopedia but refuse to pay the price-gougers on eBay.
[5 of 5 Stars!]