Pacing:
I think the pacing is fine for this game, but it would really depend on the difficulty of the modules you add in future versions.
Challenge:
I think adding in obstacles, or a specific order that modules need to be completed in could help with this, and introduce a new strategic aspect. If some modules (but not all) require other modules to be completed first, then the strategy becomes determining the most efficient way to move around the map with the given obstacles and module requirements.
Module:
The current module is fine, if a little difficult at the higher speeds.
Upgrades:
Some of his upgrades could make certain modules easier (slowing down the current module, for example) or allow Ernie to skip certain modules altogether.
Bugs:
I didn't find any.
General Improvements:
The high inertia in the movement gives the feeling of a lack of control. This could be intentional, but I think for a game that isn't about precise movement between platforms, the movement could be a little tighter. It feels like the ground is very slippery underneath Ernie. Alternatively, there could be an upgrade that improves deceleration.