My opinion on what you have so far for the terrain is, its alright... I see a lot of areas thats would be awkward if the player were to see them in game though, like stretched poly's and such.

When making terrain its easy to just make a plane with segments and then just move vertices's around, unfortunately this yields bad results most of the time unless you know exactly what your doing with every vertex (I.E. not just using smooth selection and dragging vertices's to shape your terrain) I find plane modeling the most effective way and often extrude edges to make new polys, instead of just making one solid plane and editing it all.