Re: ROMs all say bad checksum, though they play in Nestopia
If you want to play games with nestopia, here is the Linux version
(you must build from source.)
Alternatively, you can try gfceu (which should be in your Ubuntu repos)
sudo apt-get install gfceu
I can't comment on it, but people seem to like it.
My personal choice for emulation is mednafen
(also in Ubuntu repos.) and MESS