The weight of items you are carrying will slow you down, but we are also working on tweaking movement speeds, especially sprinting. Look sensitivity can be changed in input settings, while playing (not in the title screen). Also, we'll drop the default look sensitivity values for the next version, as we have been getting a lot of feedback on that.
We do have some ideas for improving jumping. The animations are probably a big part of it. We'll have to work on those.