The interesting part should be the collision code, if it's box-based etc., how you manage collisions between sprites (if applicable yet), and if you use a sort of tree subdivision for speeding up the process.
I have it running and not yet complaining about it, but I am interested in new ideas:)
Collisions are all still a bit in the working, but I created a CollisionDetector class which has an imagesCollide() method, which I use to detect pixel-perfect collisions between images. This only checks the overlapping area of two images, so when the images boxes are not overlapping, there is no extra processing.
I don't yet have collisions between two sprites, but I am using a divide-and-conquer approach to identifying collisions with the map.