There's many risk during space flight. I'm impressed with our rover track record. what many people don't realize is the martian magnetosphere is very week.
It's not strong enough to protect DNA from damaging radiation. The solar and cosmic radiation bombarding mars will need to be dealt with. We've learned how to build a life support system.. but even the ISS needs oxygen, nitrogen, and water and depends on supplies sent.
I don't think we have the technology to support a 150 - 300 day flight to Mars (all depends on time of launch).
Lets say a the mission starts when mars is closest to the earth. 150 days out. .. 10 days on mars... @ 300 days to make it home.
the mission would last at least 1 1/2 years. That's a long time to survive space. Life support systems can fail. return command module can fail.
The landing module would need to provide a shelter against the harsh martian environment. Adequate air pressure, oxygen, nitrogen, and protection against solar and cosmic radiation. The martian magnetosphere is very weak.
We need that drive we had in the 50s that lead to being the first to land on the moon. we didn't know if our astronauts would make it home then either.
We are going to need enough fuel for lift off of mars, break martian gravity and point the spacecraft to earth, and a safe reentry.
I am not sure if we have the technology yet.