As if we all don't have enough time-sucking activities in our lives. Here is a game called Capsules. There are 347 levels!!!! I have barely made a dent in the game having only completed 37 levels for a total score of 14580.
It starts off sort of simple, but gets tough really quickly. The basic idea is that you need to have the yellow capsules eat all the blue capsules. So far, the two ways you can die are if any yellow capsule touches a red one, or if you move your mouse out-of-bounds (which, seems to be loosely defined and depends on the level itself).
Some levels are annoying since they incorporate a trial-and-error guessing aspect, but for the most part most levels have been challenging and not rote. The difficulty seems to jump around a bit as it doesn't seem to necessarily get harder in order. Be warned though, you might want to pull your hair out... some of the really frustrating ones took me a ton of tries. Enjoy.
*** Edit #1 ***
Okay, I've beaten 54 levels now, but Level 55 is giving me a hard time. Going to stop for now... wow, I just wasted a lot of time. Ugh.