I really WANTED to like this game. I'd heard such great things about it, and it seemed like it should be right up my alley. Unfortunately, it was just let down.
First, the gameplay. Nidhogg has simple but slightly awkward controls that certainly can be mastered but aren't particularly fluid on their own. If you're expecting fighting-game style precision, you're going to be disappointed. Once you get past the tutorial, the movement options feel fuzzy and unreliable. The basic combat is... okay. Most actions happen so quickly that it's humanly impossible to react to them, so it's mostly about anticipation and taking risks, and be prepared for a number of frustrating deaths where it doesn't even look like you were touched by the opponent's sword.
I realize that everything I just wrote is directly contrary to what most other critics are saying about the game, but I can only call it like I see it. I've played plenty of other games in this niche, and they all felt better than Nidhogg.
The one place where the game is fun is local co-op, which is the entire point of the game I suppose, but it's fun for the "wrong" reasons. Playing with a group of friends makes all of the "screw you, that was stupid" moments fun, because you all get to taunt each other the whole time. So basically, the game is fun with friends precisely *because* of the stupid and lopsided moments that in any other situation would just be frustrating.
Claims that the game's graphics are "beautiful" are overstated. There are one or two impressive setpieces that will probably catch your eye, but the game as a whole isn't particularly nice-looking. The style is unique and expressive, but it's not objectively pleasing by any measure. Also, the game really needs a colorblind setting, because my character is practically invisible to me against the backdrop of the second stage.
My final complaint, which others have echoed, is that there's not nearly enough content to justify the $15 price tag. I normally don't mind paying a little extra for a good game, but this is definitely more of a $5 title. If it's on sale for that much and you're looking for a new game to play at parties, maybe this is for you, but otherwise you're not missing much by passing it up.