Brunni (./31) :
384px per line? That's a lot no, 320 active + 64 HBLANK?
Are raster effects possible? Parallax by moving the sprites every line, gradients by modifying the pallet…

Yes for raster effects you can modify background color, x sprite pos, y sprite pos, sprite tiles, x-zoom, y-zoom, x mirror tile, y mirror tile and choose *which* palette you use per tile. You can only do sprite changes per line as far as I know (not during a line) because sprites are parsed a line or so before they are displayed. A game like Riding Hero uses raster effects most obviously for the road and Neo Turf Masters for the line scrolling on the psuedo 3D display. Some of the fighting games use it for the floor too.

You can't modify the palettes themselves (apart from during Hblank and vblank) because the palette ram shares a bus with the CPU. I read that the color the Neo Geo displays to the screen is what you are currently reading/writing with the CPU from palette RAM. So you get a messed up display if you read or write to palette RAM during display. There is probably enough time to make some palette changes during Hblank

I don't fully understand why the 384 myself. But here is what it says on the wiki :