The base game is okay at best.
There's no innovation in the play experience, and the UI design is not noteworthy. It's a simple game with simple functional features. I do wish there was a separation between noting potential numbers and filling in the one selected as the answer. I don't like clicking around more than necessary to get my answers to register.

More than $86 to have all current DLC puzzles is outrageous.
I did all 30 base Easy 4x4 puzzles in about 15 minutes, so paying $3 for another 15 minutes of entertainment is out of the question. Only the "Easy 1" groups for all difficulty sets (4x4, 6x6, and 9x9) are available in the base game, so higher challenge levels require paid DLC, which seem to unlock 30 puzzles each.

Not all of the DLC has been released, but what is available and announced for the future will total to about $146 at full price—$43 if you're someone to wait for sale prices, which is still absurd. The full-game experience feels like a complete money grab. I'd rather get a $3 Sudoku book at my local gas station as I'd get far more puzzles for my money.