Picked up Planetary Annihilation on early access now that it's dropped to a reasonable £30. The game is amazing, I'm just terrible at it and there's no difficulty options for the AI, so I'm usually just on survival turtle mode until I get a massive Nuke dropped on me.
But my recommended games so far would be...
Tropico 4 (one of my favourite city building games)
Sleeping Dogs (super fun game, need a decent PC to run it well)
Terraria (1.2 update is awesome, it's like a whole new game, so much more playable and fun than it was before)
Skyrim (standard edition, not legendary, it has great mods which are better than the DLC content)
...and remember, don't buy it unless it is at least 75% off because if it doesn't get that discount in this sale, it probably will in the next one, or it might be in a flash sale at some point.