The problem with the current RX-8 is that it has only about 230HP while the competing Z-370 puts out 330 and the V8 Mustang puts out over 400. It gets worse gas milage than the V6 doing it, too. It will be interesting to see what they come up with in the 9 and if they finally get competitive with pistons. Gas milage has been one of the biggest weaknesses of the design, from what I can tell. It's light enough that they could put a bigger engine in and presumably match the power output of a piston engine, but the milage would be really bad.
They have done a great job on the styling at least. The current RX-8 was not ever a really cool looking car IMHO. 