my interpretation is thus: It is very similar to the 4 stroke, 2 stroke debate, as rotary's operate as essentially a 2 stroke. Thus while they can burn a lot more fuel per second, and hence get more power, they do so inefficiently. This has become a problem with changes in emissions regulations. However practically you can get a lot of power out of very small displacements, and hence get fantastic power to weights. Similarly because of the large amount of fuel they can burn, they couple with turbo induction very very well. A typical downside is things like that the whole central rotor has to move, and so there is a lot of friction wear on the seals, which has given it a bad reputation (I think) for reliability. Overall many companies and individuals worked on the rotary concept (mercedes, nissan to name a few) however only mazda continued for such a long time (rather like wankel). They certainly have some great positives, but also a number of downsides, which is perhaps why they have never been largely taken up. That's just my rough overall summary of rotaries .