Looks very pretty, as does the semantic markup. Personally I'd prefer it if there was a little less alpha, e.g. on the Malta pic the text isn't so clear...
I just had a play myself and I like somewhere between 0.8 and 0.85. I'm not a designer though and lean a lot more towards clarity vs style.
When using it I wouldn't want to have to manually pick a theme based on the pic, as it would probably be a database gallery - but a choice of themes is great to have.
Do you think it would still be better to bump the alpha value up to 0.8 or so?