The people who are into is do things in the game that people do things people don't notice. For example, do you know that you can get 10,000 by clearing off all of the blocks on the screen? It sounds easy, but it's actually pretty hard. Try it =) And 1,000 points for only having the same color blocks on the screen. See for people who plays it casually, they only want to survive as long as possible deleting the blocks, but that's so basic that's it's not fun. The fun is when you start doing advance stuff like clearing all blocks from the screen, and having 1 color blocks on the screen. Also having high multipliers of blocks (clearing 15+ blocks at once).
The game is really genius if you can take it into another level. At the very basic level, lumines is actually quite boring.