It's a simple ISA, but built to be fast. It's specifically designed to map well to OoO cores at the slight expense of some features on in order cores that give you little boosts (like branch delay slots and other exposed pipeline features). Last I saw, BOOM compared very well to other OoO cores at the same gate count.
If anything I think RISC-V is repeating the same mistakes as MIPS and the original RISCs, by being far too simple and requiring much greater fetch bandwidth in the process.
The performance of MIPS, which it is closest to, has never really been considered anything more than "acceptable". It loses to ARM (which isn't so RISC-y anyway) and x86, so I expect RISC-V to be about the same:
