there is soooo much misinformation in this thread, its not even funny.
where to start...i guess fuel economy
the fuel economy of rotaries has been increasing with each generation. the first rotary engines got pretty bad fuel economy, but then again, so did the first piston engines, but like Mako said, they actually get close to the same gas mileage as similarly powered boingers.
The FD (when not driven at WOT) gets around 15mpg in the city, and gets 25-27mpg on the highway. The RX-8 gets around 18mpg in the city, and around 25-27mpg on the highway. Compare that to the V6 Accord, which gets around 19mpg in the city, and 28-30mpg on the highway. Not that much worse.
There are 2 problem areas for rotary fuel economy. one is the shape of the rotor...it creates a long combustion chamber. and at high rpms the a/f mixture might not complete combustion before exhaust. but this has partially been addressed by the firing order of the plugs. second problem is primarly limited to FD and prior rotary engines because exhaust gases were able to leak back into the intake "stroke". Changing the port locations on the rx8 all but elimiated this problem.
and to the person that asked about compression, its not 13:1, but the renesis engine in the rx8 is 11:1. pretty close.
also considering the piston engine has had developed over 100 years and by every automotive company out there and the rotary engine has had only half the development time, and only 1 company, the rotary engine is doing remarkably well. try to imagine where it would be if it had the same development resources as the piston engine.
Oil usage, yes, rotary engines do burn oil, and they are supposed to, as that is the source of lubrication for the apex seals. the rate at which they use oil depends on how hard it is driven, but typically on older rotaries it is 1qt/1000miles, and on the rx8 it is 1qt/3000 miles. Although, Mako was incorrect about the rx8 having a seperate tank for the oil that is injected into the engine. the oil metering pump draws the oil injected into the from the regular supply.
Both the apex seal failure and overall reliability can attribute to improper tuning, like Mako said. And even then, it is mainly related to FD. The FD is an incredible car, but it did have some flaws, mainly being inadequate cooling, especially considering it needed it the most because of the twin turbos.
Take the FD out of the equation, and the rotary engine is extremely reliable. It is not uncommon to hear about FBs and FCs with over 300k on the odometer. Compared to a piston engine, the rotary engine is extremely simple.
now, on to power. the rotary engine produces a very flat torque curve, so, even though it doesn't make all that much torque (comparitivly), it makes it very low, and maintains it. For example, the rx8 produces about 130ft/lbs of torque at the wheel peak, but its making 125ft/lbs by 3.5k rpm. That's more than most econoboxes make peak. and no one complains about econoboxes not being driveable. Fact is, rotary engines are very drivable on the street.