I don't think the US has any interesting planetary missions planned for the future. This doesn't include the Europa Clipper which is just a proposal at this point.
I think OSIRIS-REx is less compelling than Hayabusa 2 and the
New Horizons New Frontiers program money could have been used better to fund a Jupiter Trojan, Io mission, Venus orbiter/lander, etc. instead.
InSight is
another Mars lander based on Phoenix to be conservative and safe with the design. It will study the Martian interior like never before, but there's been too much attention spent on Mars. The Discovery program had two far more inspiring competitors, but the
ASRG program was halted.
The 2020 Mars rover is a clone of Curiosity which is, again, not very exciting. Its payload is focused on remote sensing instruments to quickly analyze interesting samples that may never be launched to Earth. The inclusion of MOXIE seems ridiculous and is only necessary to achieve a TRL of 9 on that kind of instrument. If there was more funding for the science payload, MOXIE could have been replaced.
I already mentioned Hayabusa 2 which uses ion engines and many landers and an asteroid impactor in the spacecraft's design.
Meanwhile, Europe has BepiColombo. Like the Japanese mission, it will use ion engines. It will study Mercury in more detail than MESSENGER can, a planet that has not been explored much.
Europe's JUICE mission will examine some of the ever increasing number of known liquid worlds in the outer solar system. It will
orbit Ganymede and yet not forget about Europa and Callisto. Europa has a better chance of harboring extant life than Mars. There will also be studies of Jupiter itself, so the spacecraft can be considered the successor to Galileo.