I'm using IE 6.0 as well, its a new computer (or a 6 month old computer, which is still fairly new). And supposedly a fast CPU.
Its way too easy on my screen. Each tile takes up to 5 seconds to drop. I think that speed options would help. Is there a way that the game could speed up as time goes by? Those are always challenging.
The other thing I found, may be hard to explain. If two identical tiles land next to each other, they disappear. If there are 2 tiles the same touching diagonally, and a third falls to complete the L shape, all three disappear.
If one tile disappears forcing another to drop down into a space adjacent to an identical tile, nothing happens. If a third tile lands beside these two, only one (directly in contact with the new dropped tile) disappears.
However, if a column has a tile sequence a b a, one on top of another, and the middle tile, b, is taken out, you get a column with two identical a tiles one on top of another. Then if another tile the same drops on top of that, all three disappear.
These seem to be minor inconsistencies. I don't know if you can change anything, and its certainly something the player can get used to.
Can you tell I play waaaaaay too many video games?