Here's a link to a gaming site (Gamespot) that lists their best choice of games in the Steam sale under $20/£20
Link It may give you some ideas.
Of the games listed I bought Vanquish and I can only say that's my kind of game - a brainless shoot 'em up - yee-hah! It's a bit like the Gears Of War Series.
I recently bought The Phantom Pain (From the Metal Gear series) on disk for Xbox One for £8 and was very impressed with it so I've decided to buy it for PC in the Steam sale for £12.49 cos I can never get used to aiming and shooting with a game controller with the Xbox 1 so would prefer to play it on PC with mouse & keyboard.
The game starts with lots of cut scenes but eventually settles down to some solid gaming with mild stealth elements and some intense moments. I will take the Xbox 1 version back to the GAME shop and part-ex it I think.
Also on Xbox 1 recently I played the demo of the beta version of Ubisoft's The Crew 2 and it was pretty good. You get to drive Cars, Motorcycles, Boats and Planes and the cars are especially good whilst I personally was crap at the planes I kept crashing them but I've never been any good at flight sims, not even arcade ones. The planes are pretty much a mimic of the Red Bull plane racing so if you fancy yourself as a bit if a wiz pilot, worth considering.
At Abarb's suggestion I will buy Cat on a diet for 39p as it got good reviews, nowt to lose really. And I couldn't get your first link to load for me Abarb
Talking of Cat Games, I also recently bought Cat Quest in the Steam sale and it's ok but it's really a bit of a kids game.
Finally, another Steam sale question: Anybody played 5 Nights at Freddys? If so - what's it like? The first one is up for grabs at 99p and the other 3 are currently £1.44 each.
The Steam sale ends on July 5th.