Only way I could see myself buying Crackdown 2 is if they put female characters you can use.

Flash may not be the best option, especially if you want to have 3D elements, but there seem to be some pretty amazing game engines around these days that could reduce the amount of work involved.

I totally agree with the part about doing it for love rather than trying to get rich, though.

This seems to be a great idea,around here we don't have many programmers or game producers.
The logical suggestion would be a simulation or a side-scroller,which I support,however,maybe we should branch out a bit?
Perhaps a 3rd person genre action-adventure or fantasy game?Something like a Tomb Raider Amazon,or an Oblivion like game.I know this is really far-fetched,but who knows what could happen?These fantasy and exploration games usually sell well,regardless of the protagonist,but I'm just suggesting stuff because we shouldn't limit ourselves to one or two genres.
Also,an artist on DeviantArt has started a side-scroller project,here's a link:
http://blackkheart.deviantart.com/art/Beautiful-Brawler-Beta-0-1-134798064
It looks good so far,but nothing growth related.