So Dr. Luigi is pretty cool. I'm disappointed that there's absolutely no story mode like in Dr. Mario 64. Not because of the gripping narrative, but because of going through stages battling progressively harder CPU character that actually had some personality (like the sounds made when pulling off combos or getting combo'd). And at least rudimentary unlocks like secret characters and challenges such as beating the story mode without dying on different difficulties.
That said, the two new modes are both pretty crazy. At first I thought the stylus mode was basically just an alternate control method where you manipulate the pills with the stylus. But then partway into a level two pills start dropping simultaneously. Then three. You have to multitask and arrange them all before they hit the bottom (they fall slower than usual). There's actually way more depth than apparent due to being able to exploit the various timings of things happening. Also, when you destroy a column that causes adjacent pill halves to fall due to how you stacked them, you can now re-arrange the falling pieces as well (normally they fall straight and you have no control). Mind blown.
The Luigi mode with L-shaped pills is also awesome. Basically instead of getting a single pill dropping, you get a pair of pills glued together in an L shape (like the Tetris block). It took me several stages to wrap my head around proper strategy, and I thought it was way harder than the regular mode, but suddenly when it clicks it's actually a lot easier. The reason being that you can often clear things in bulk. You end up having to drop incorrectly-colored pill fragments more often, but they're way easier to destroy because each L you get has three pieces in a row of the same color (the game seems to be designed such that the long part of the L is always a solid color). I got to like level 36 showing no signs of losing before stopping for the night.
So yeah. Loads of fun.