Matthew Brown's Hexcells is great! That's the most important thing that needs to be said about the game, but I suppose I'll expand on it a little more.
For the uninitiated, Hexcells is basically Minesweeper meets Picross with a tiny sprinkle of Sudoku. Your only controls are to either destroy or highlight an orange hex with your mouse cursor, and the goal of each puzzle is to destroy/highlight all of the orange hexes using the numerical hints given to you. The starting hints are simple—the numbers inside of destroyed hexes will tell you how many highlighted hexes surround them. You can see this in the screenshot down below:
This puzzle is easy enough that it can be solved through cursory deduction. If you're a Minesweeper amateur like me, the game thankfully eases you into its basic mechanics early on, but be warned: it'll turn into a brain-busting mess before you know it! The first Hexcells game is relatively straightforward (it took me two hours to "perfect" it), but the following Hexcells Plus and Hexcells Infinite took me 10 hours each to plow through. More hint types are piled on as you progress through each game, and the way they shape your comprehension of the game is pretty astounding.
Talking about numerical puzzle games like these are difficult, because you'll either like it or you won't. If you're looking for a twist on the Minesweeper or Picross formula on Steam for an absurdly cheap price (all three games can be bought for under $3 during a sale!), then Hexcells is a no-brainer. I had a damn good time with it!