A platform game (even a simple one) tends to be much more complex than Tetris. First of all, you''re probably going to need a lot more graphics. While Tetris only has square blocks (which, I assume, anyone could draw), 2D platformers generally have lots of animations (walking and jumping, at the very least), as well as terrain types for the blocks (grass, dirt, etc.). You''ll probably also need some (simple) AI for the enemies, which Tetris does not. You''ll likely need a level file format, and level editor to make levels.

This is just the tip of the iceberg. Obviously, there''s quite a bit more involved with a 2D platformer. I''m not saying that can''t skip the ''standard'' game development steps - Tetris, Breakout, etc. - but you should realize that you may be getting into more than you realize.