Cool job so far. If I may, I'll give you some criticism. Feel free to ignore
It seems that you got a bit of a design problem. Judging from the screens, the man-made structures all look great and very realistic, but the looks of the terrain sets the map back alot. There is no really easy way to 'fix' this - it has to do with the theme you've chosen. It's not standard to Crysis to have large outdoor snow/ice landscapes. All the frozen singleplayer levels that came with the game were relatively confined areas that were heavily filled up with brushes and non-natural objects.
Getting a snowy, wintery landscape to look good in a video game is usually a tough job. When focussing on your map, I can say that the problem is terrain shape and contrast. Shape, because the hills do not look like they are made of snow/ice. Their slopes are very steep and look fabricated rather than natural. Contrast, because you're dealing with the colour theme 'white' here. In order to make a map visually pleasing it's a good idea to always add colour and contrast. Most large outdoor winter environments therefore have very dark brown or black cliff textures that contrast the overall whiteness. Colour is usually added as cold blue global lighting, contrasted by warm yellows and reds for these type of environments. The warm colour lights are usually added around fires, static lights, human buildings, etc. Take a look at how other video games did it to get an idea how to make your map look.
So, to get your terrain to match the visuals of the rest of your architecture, you will probably have to completely re-do the terrain. If you are really down with that thought, you could consider this project a learning project, move on, and re-use it's assets in other maps you will make. If you ARE going to build wintery landscapes I would suggest nog bothering with the layout of a real-life island (since when did video games start caring about reality?
). Also, generating these kind of heightmaps in a terrain generator can be a huge help. World Machine 2 is about to be released, and it has the ability to instantly simulate large snowfalls on terrains. Check these pics for example (taken from the World Machine development blog). Something like this would help the looks and overall feeling of your map alot.