Completely broken and shallow.
The gameplay is as expected in a modern first person shooter, except now with power-ups called "Mods." Mods allow for different types of power-ups that either make you faster, allow you to take more damage, carry more ammo, etc. They do add a small bit of variety, but most require a lot of playtime to unlock so the variety is sparsely seen. Controls are just as one would expect, and work just fine.
The game boasts a nearly non-existent single player and I am dumbfounded that it even exists. It lasts for only four short missions and the only purpose seems to be for unlocking weapons to use in the multiplayer mode. These missions can also be played in online co-op so you and a friend can blast away bots together. It's also worth mentioning that the single player missions are nothing more than muliplayer matches with bots minus the multiplayer. Once again, I question why they even bothered adding it to the game.
The multiplayer mode in Punisher: No Mercy is clearly the focus of this game, but it's unfortunately a wasted effort. There are only a few modes to choose from (Vigilante, Team Deathmatch, Punish the Punisher, Elimination, Time Trial, Survival) and they have all been seen before. All of this would be fine and dandy (especially at $10) if the online system was not completely broken due to lag. Every match I attempted to join (which took some time) was extremely laggy to the point of unplayability, which renders the game useless.
It's unfortunate that the developers of the game did not focus all of their energy on the multiplayer aspect of the game, because that's clearly where the game's legs are. Due to that unfavorable approach, those legs are broken due to the consistent lag experienced in the game. Unless they release a patch to fix the lag, I can only advise to stay far away from this game.