Hmmm... just my humble thoughts so far
- I'm not from River policy or anything, but your map seems to be missing more rivers. A lot more of them.
- If the planet's supposed to be Earth-like, as you say, you'd invariably need to at least have a wild guess where your tectonics are to form mountain ranges and alike. You could simply look at Earth tectonics for ideas
- The "center" continent looks a lot more blurry than others