Really liking this so far. I got stuck on the second part with the Terrascanner, though.
It told me to use it at the locations marked on my map, but I don't see anything on there so I didn't really know where to go.
[edit] Found a bug.
Figured out where to go by myself, and used the Terrascanner/bombs. Got to the bit where you find out you can use the grappling hook as a zip line. I was stood on the very edge of the platform when I did it, hit [enter], and the guy "stapled" it in mid-air (it was a good 20 pixels or so to the right of the platform, but it stayed there), then I automatically fell off the platform into a pit full of water before I had a chance to do anything else.
Had to restart the level as I couldn't figure out how to use the zip line after that (I fell into the pit a further eight times, trying to work it out), as I missed the rest of the instructions.

[edit again] What are you meant to do when you're out of ammunition? I did spot what looked like some ammo boxes early-on, but I couldn't get to them because a massive snake thing came out of the ceiling and got me. I haven't seen any ammo boxes since (though I have learned you can get passed the ceiling snakes by swinging past using the grappling hook).
As it stands I'm far into the second part, closing in on some dude with a tracking beacon, but I'm out of ammo and things keep killing me because I have nothing to fight back with. That's gonna be a problem.