I had trouble enjoying the game when I first played it years ago, but the more I played it the more I liked it. The style is very unusual too, I kind of hated it all at first, but now the charm has really sunk into me.
This really was one of the weirder experiences I have had with a game recently. I really recommend it though, even if it seems overwhelming and awkward at first. The multiplayer is also especially fun if you are playing with a group of people you know who will not take the fight too seriously.
On the topic of exclusivity: Microsoft has had a deal with Treasure Co for quite some time. They are set to make Radiant Silvergun 3/Ikaruga 2 for them along with a few new games and more ports. I do not see this changing anytime soon, but I doubt Vita is part of this contract (wishful thinking?).
I hope SEGA publishes their next few games though, Radiant Silvergun had an outstanding conversion and I literally never see anyone talking about it. This really, really makes me sad.