I've done it alone, aside from sounds (got them from
Freesound, I mixed background themes later in Audacity) and music (You can find it
here. A lot of great music). Working alone is really challenging - a lot of different stuff to do. I've learned a lot, but wasted a lot of time because of poor planning on my side - changed graphics 3 times, spent time on boring/unnecessary features etc. It lacks a few features, but it was taking too long so decided to publish it. Now I test my ideas beforehand, so I won't waste time for things that don't add fun to game.