Should we try and be secretive about what we're making, and the next developer doesn't know what they'll get until they downloaded it? Or do we give pictures and titles, so that the next developer picks what they think is interesting?

Personally think it might be fun to use a title that tells people vagely what the game is about but doesn't give too much away

Just don’t try to make a completely finished game unless you’re on day 6 I guess. Always leave the game open for changes that other devs can make.

Id say leave the title for the later day devs, and just give a brief, vague description of what you have made (as not to force the next dev into the exact framework you have in mind and allow for creativity on top of what you have planned).