I have to say before I start that variations III and IV were my favourite, and I dont really know why
Now I know nothing about organ writing, so this is more of a listeners view, and is pretty much subjective to my opinion.
Personally I felt that throughout some of the piece it lost that regal atmosphere that 'rule britania' contains. Likewise it felt at times a bit, for lack of a better word, forced, in some of the ideas for transisitons etc...
Keeping in mind that these were purely personal opinions...
Generally I think that you did very well with some of the variations and I enjoyed listening to it
Lex