For me, I'm spoiled, any discount below 75 % is way too small.
Best discounts are when the long awaited game is pay what you want together with other good games.

Completely depends on the game. for some 50% is a great discount. For others im in a similar boat and look for really deep sales.

Much depends on the game, actually. If the game is rumored to suffer from some problems but tempts me, I'm likely to wait till I find with a 70%+ discounts. If it's not exactly my style of game, but just something I want to try yet is technically ok, I'm going to wait till it retails with a 40-60% discount. If it's my style of games, expected etc. I may not wait, or I may, but the discount is not the main criteria, just a welcome bonus.

For me it depends on quality of the product and the base price.
50% on a $60 game might not tempt me, but 50% on a $10 game might.

Really depends on game and base price.
I consider everything over 50% as good but it doesn't mean I can't go for lower discount nor that I will buy everything with higher than 50% discount.

50% Half price is good enough to me, 75 being the best i expect.

75% will usually grab my attention in any case, because for the majority of games, that's the level on which they bottom out. When a game is offered with a lower discount, then I'll expect it to go down to 75% eventually if I wait a bit. I might still be getting it, but it depends on:

a) actual discount (60-70% are still pretty good, whily I typically won't touch anything less than 50%)
b) actual price (When the list price is low already, the difference between a 66% and a 75% discount becomes negligible)
c) whether I intend to play the game right away (If I'm just going to add it to the collection, I can easily wait for a better offer)
d) whether the discount seems exceptionally good given the game's age and previous pricing policy

Kinda depends on the start price.

Its a rare game i am willing to pay even 10€ these day, thanks to all the bundles and thus backlog. Let alone gog/steam sales.

I only buy 75% off games on Steam (and usually 60% off on GOG).

60%-75% will make me buy when I haven't had a strong urge to play it before.

Any lower percentage than that for something I'm actively seeking out is a good discount for me.

Yeah 70+% is my ideal.

I refuse to buy games which aren't at least 60% discounted. 50% seems to ordinary :P... But above 60% depends on the game. I'm beginning to be picky lately because my backlog is getting large already.

As long as the game is below $10 I'll probably pick it up for myself. If it's something I really enjoyed and for whatever reason is in the $2-3 range then I'm snagging copies to gift to other folk.

Percentages don't mean jack. I don't pay a percentage, I pay an amount of money. I couldn't care less about how many percent off a promo sets (or whether there's a promo running at all), as long as the current price is one I'm willing to pay for the product offered (and that in itself partially depends on my current mood).