Your rivers are rather off. I would recommend reading through this thread to get a better feel for river shape and placement. Basically, you have problems because you show your rivers forking (which does not happen on a large scale).
As far as other things to add, I would recommend adding mountains. These should work well with a re-evaluation of river placement, as rivers always flow from highlands to lowlands. The overall shape of your map reminds me of an impact crater - if that is the intent, perhaps add a bunch of mountains on along the inner sea which were thrown up by the blast?

-Seleucus I