This has been my go to shooter for a loooong time now. What makes me come back to it is the movementsystem and the tight controlls. You can really do some amazing trick jumps, including walljumps, rocketjumps, rocket-walljumps, grapplehooks and all that good stuff. The thing is, the game does a really bad job of teaching you that you can do this. So the game doesn't make that good of an first impression. To go fast in this game (and belive me, you can go really fast in shootmania) you have to put in some time into it. The mechanics are very unique and takes a while to get a hold of. It has a style of it's own and no other game plays like it.
On top of this, it allows player to create new maps and game-modes, items, characters, skins, weapons and more, so it has a ton of content, and there are allways new maps and modes.
There is a really good arena fps here, but it's hidden under some pretty bad menus and the lack of tutorials certainly doesn't help. So you may have do watch some youtube clips.