Well for the indicator's sound it is common to both difficulty levels and you now have a sound as to the direction you should take is up, left or right, and each got its own sound. About math games the only thing that was changed is that you start directly from a high level of speed and you continue without any breaks between each 3 math problems. This is not a big deal as I managed yesterday to score 160 in the subtraction game at HC. Here are some other differences:
Salt unloading: There are 2 camels instead of 1.
Crush the moles: moles are a bit faster.
Waterworks: waves move extremely fast.
Mortal swamp: the quick mud is vertically larger.
The snake to charm, the snake is a rocket rather than being a snake, you whistle for no one, plus a 2 by 2 solid squares I think.
Simon: The sounds are faster.
Labyrinth: some more obstacles across your way.
The queen's treasures: The guards are faster, and they often spawn other ants so fast, ones that track you no matter where you are.
Searching for pheromones: There is a whole ant army, and you gotta find your way out alive if you can.
Mastermind: a new color, indigo.
Eels' haunt, stringrays pit, dangerous beach and basically any beach game that has enemies: crabs, stingrays, jellyfish and eels are extremely fast.
Fire: the pitch is sometimes changing and I was burned while normally turning it off for an unknown reason.
Rainbow: They're basically moving in all directions rather than just one.
Rolling balls: You have an additional ball, giga minus.
The nail game: the nail can break if you overhammer it.
Boreal forest: the enemies are much faster, especially elks.
Perilous corridor: the pits seem larger, plus the fireballs are moving faster and there are slippery areas as well like most of the hardcore games that have pits.
Stopwatch corridor: you have less time to walk past doors.
Mushrooms' path: Mushrooms occupy vertically much space.
Frisbees games: nothing more difficult I'm afraid.
Princess's aquarium: there are more snails, and less distance between each 2 so be careful not to kill the good ones.
Locked bonuses: bonuses are protected by 2 doors instead of 1 so you better search for more buttons and have more patience.
The house that makes you crazy: 3 floors instead of 2, each containing 6 windows as far as I have played.
Cursed place: I hope that game doesn't become harder, it's already as crappy as hell 
.
Robots swimming pool: robots are faster.
Zombies and ghost games: these undead and ghostly creatures are a lot faster, but that means for me that I can kill them more easily.
Trolls' games: they are no longer as slow as you have seen, and you will start running across groups of them in the troll's enclosure.
Peaceful mountain: some slippery places and faster winds and wasps are everything as far as I can tell.
Bouncing ground: pits are so, so near to each other so you can't distinguish easily when to jump.
fire clouds: faster fireballs, larger pits and slippery areas.
Measuring trees, too many trees to examine.
Pasturing the camel: less grassy areas so you better know where to get your dear camel.
Cut down the cactuses: more of them in fact, as for the path the only difference is that it is a bit longer than usual.
Falcons snapshot: falcons are too fast so you should time carefully when to take the photo.
Drawing on the sand: in most cases the grid becomes a 6-by-6 grid.
Drip drop: 3 faucets instead of 2, and varying water pitches.
Cold river: less slippery places and more walls.
Transport the penguin: the penguin is so quick and he knows how and when to escape sometimes.
Peaceful descent: literally quite a lot of rocks to avoid.
Snowballs road: a lot more, yet faster snowballs.
The bears games: there are a lot of them, in crazy speeds as well heading towards you.
Giant snowball: just harder to completely make in the allotted time.
Flying boat: cannons always throw extremely fast cannonballs so you better know how to dodge. Lol we even got a pit located on the wall today in a minigames server so we got to a dead end.
That's all what I have found so far, feel free to add any of the games I have not cited.
