go for quad trees , for your map system and speeding up your collision testing..

most of the best selling 2d games aren't really highly
complicated dense graphical scenes , the important
thing is to have a good concept with good mechanics.

start with a simple prototype and drop it early if it
doesn't feel good , if it feels good then you might
just have something , most people aren't the type who
would sit down and play something complicated or big ,they just want something to pass the time with and feel like they are able to play and understand it,
this is why super mario and simple games like minecraft had wide spread success , no serious gamer looking for eye candy would bother with it but
then again not everyone is seriously interested in
technical eye candy .