RefleX, originally released in 2008, must be one of the better games in the Shoot 'em up genre.
I might not be the biggest fan of the genre but I still had a "Blast" playing the game.
The gameplay is just what you would expect in a game like this; It's fast, enemies shoot you from every direction and it's pretty difficult, in my opinion. One thing I really liked is the fact you can use your shield to bounce enemy bullets back.
Since the game is pretty old, the graphics and music are straight out of that era but that just adds to the charm of this game. There are no online leaderboards or achievements, so you can only compare your own scores.
A game like this is not for everyone but I can recommend this to every fan of the genre.