Despite my good will, I ended up tuning the code structure more than expected, and didn't come up with an operational Tetris game yet. Thing is not that I fell into the engine development death spiral, but rather that I touched the code very rarely along these weeks, with no solid design approach.
Anyways, I've been working on a small architecture which separates input handling from graphics handling, along with a simili-2D-engine which features - so far - simple rectangles, loaded images and text rendered from TTF.
I must say that too many design doubts and questionnable perfectionism hamper my ability to simply write the code down, though I'm working on it.
So, that was just some information about the progress, linking a test picture of what the graphics can handle:
(click for full size)