1. Give your text content a little more space around. Some padding to the left. This will make it more readable.
2. Your left menu bar is too long and the actual "sub menu" items have more visual weight than the principal ones. You can try to switch the background colors. Also, you may want to use some spry menu or reduce the size of it.
3. The green monochromatic scheme is nice, but then your pictures are too colorful and the english/spanish flags too. They just call too much attention to themselves. You have more important content than the language options. It's better to give the contrast, the colors and the attention to the content.
4. The changing pictures are kind of distracting, could be better to have only one, big, beautiful picture and then a photo section.
5. Following the standards placing your logo on the top left wouldn't hurt.
I'd just add that it's quite important to try to follow worldwide web consortium web standards, see http://validator.w3.org/
This will give your site a chance of appearing fairly consistently on varying browsers and operating systems. It will also be a start towards meeting accessibility requirements, so that users with screen readers or on specialist equipment can use your site.
At present this site fails with 269 errors - quite a large amount! Most of these will be easily fixed if you work your way through the validator's error messages.