This really wont help make it fun, but what about using free assets you can find online?
Where can I find free sprites and images?
Where can I find free music for my game?
For For making levels, what if you could generate them via code? This wont work for all types, for it does for some games.
If you just can't stay motivated through it, what about paying someone to do it, or teaming up with somebody? For me, I do all the coding and a good fried of mine does the art, story line, etc...
What about breaking it up into more manageable pieces? Maybe tell yourself you will do 2-3 levels per week, and if it takes you 3-4 weeks to do them so be it. At least you finished! I find this helps me a lot on mundane programming tasks.