Move Agent 47 on the grid and either avoid or kill enemies to reach the exit / kill your target. Each level has 3 goals; completing the objective and then 2 other challenge conditions which sometimes can be done at the same time, but are often mutually exclusive. For instance a common goal is to finish the level in a maximum number of moves which you wouldn't be able to complete at the same time as killing every enemy (another common challenge goal). Moves aren't timed so you can take as much time as you want to consider your options.
There are only two minor things which occasionally annoyed me.
The angle your character move changes based on the position of the camera (which you can move using the right stick). This isn't an issue when the default camera position is like the above image where the grid lines are parallel and perpendicular with the edge of the screen. Occasionally though the default camera position is turned 45ish degrees for some reason, in which case there is a 50/50 chance pressing right might make Agent 47 move to the right or up depending on whether the default camera position is turned 43 degrees or 47 degrees. If the camera is twisted like that, to ensure accurate moves you either have to move with the touch screen, or use the right stick to twist the camera back till it's parallel/perpendicular to the edge of the screen so you can make your move. The camera stays locked in its default angle so if it is cockeyed you will have to manually twist the camera each time you move.
The other issue I had on some of the larger maps is when you are near the top of the level, it is difficult to see enemy patrols at the bottom of the map as you can't turn the camera a complete 180, you can only turn it about 100 degrees.
There are around 90 levels and those two issues only happened about 5-6 times so it isn't a big deal, but it's a shame they didn't fix it somewhere along the line considering this is a port of an existing title.
$6.39 is probably a little steep considering it is a port of a mobile game. $5 seems about the right price to pick it up. No performance issues on the vita other than sometimes the small screen makes it hard to see which direction some of the guards are facing near the back of the map.
Just remember not to use hints by pressing triangle or you'll have to reset the game to get the plat. Otherwise nothing else is missable.