Welcome, Jay!

The concept is quite agreeable; nothing entices exploration like a map with unexplored regions!

First, though, some river corrections:

-On the eastern peninsula (the southern half), there is a river starting on one coast and ending on another. Unless it is a very unusual type of canal, the river should only touch the coast once.
-The lake on the western side of the landmass has rivers extending towards two different coasts. While it is not impossible for a lake to have more than one drain, they usually just go in one direction.
-There is an odd situation going on with the rivers on the upper half of the eastern peninsula, with one river spreading out into the land and another forming up nearby. Seems like there should be a swamp there.

Save for those two details, everything else seems in order.

As for the feedback, let's see:

-Cities: Since the idea is to leave lots of blanks and territory to explore, I would try to designate a region of the map to be the "untamed wilderness"; the western half of the map seems ideal for this, with lots of room for expansive jungles/wind-swept deserts/etc. So I would put two cities on the eastern peninsula (the large bay seems like a good place for a port, well protected from the ocean), and a third, smaller city on the end of the river steeming from the lake, as a sort of colonial stop for those adventuring into the unknown.

-Land Features: It would be a good idea to put some kind of landscape/climate cues, like dunes for deserts or pines for cold forests.

-Out-of-Place Features/Mapping Violations: Other than the rivers mentioned above, I think everything looks pretty consistent and reasonable.

Keep up the good work!