It's the whole game, but not with the highest-quality art and sound assets available, though that is set to change.
I bought the Humble Android Bundle and own both.
The PC Version has higher-res graphics, so you could say it takes full advantage of the bigger screen.
There's some direct info in this entry on Tiger Style's blog
You can also buy Waking Mars for Windows, Mac, and Linux directly from
us on the Waking Mars website! We’ve said it before, but the game
surprised even us with how natural it feels on PC. Kicking back on
the couch holding a gamepad watching it on the HDTV was a proud
In addition to the regular technical and controls type work that goes
into a port, we massively upgraded the story presentation. Check out
the improved character portraits, below. We also added professional
voice acting which we’re really pleased with and we’re glad to see the
critics and fans digging it too!
We don’t like to be stingy with our iOS roots, so we ported over all
this voice acting and art goodness as a major update to the iPad,
iPhone, and iPod touch versions. It’s almost like a whole new game,
and as always App Store updates are free, so download and enjoy today!
Additional to that, this tweet,
Waking Mars on Android does not have voice acting yet. It's in progress but no ETA yet. Watch for updates here., indicates that the higher-quality assets will ultimately become available on Android too, but you might have to wait a wee bit.