The strength of Lilypond lies in the code. It would be hard to make a really usable GUI that hides the code, without simplifying things. As already suggested, use a good editor with it (I use Vim, but jEdit is a good alternative with with some lilypond-specific stuff). Basic note input is actually easy and fast by hand. Once you have some macros and templates set up, starting a new score is rather painless, and basically involves just typing the name of the piece and then entering notes.
Learn Finnish, part 1:
ice-cream cornet: jäätelötötterö