I first played Ikaruga for the GameCube and instantly fell in love with it. At first I treated it like any other shooter before I even started learning how to chain combos properly. The combo system is where this game really shines, it turns from a "shut your brain off and shoot enemies", to a fast paced twitch puzzle game. I've spent countless hours on the GameCube version of the game and the PC port holds up well. When you get into the groove of the polarity switching and memorize enemy patterns there really is no limit to what you can do next to improve your score.
What kept me playing is i never felt like I’ve hit a plateau in what kind of score i could achieve, there is always positive reinforcement to keep playing because you can see what the guy ahead of you on the leaderboard has done... don't go way above your means and watch the number 1 player and think I’ll never be able to do that... watch the guy who's only 2 million points ahead of you and mimic the style he's using... you'll quickly learn that the game that's touted as "impossibly hard", is actually very doable to get a high score.
I recommend giving it a fair chance turn the BGM off and play some of your own chillout tunes and enter the meditation that is Ikaruga.
-very forgiving hitbox often times you feel like "how did i just survive that?!", rather than "oh man how did i die there!?"
-mesmerizingly intelligent level scripting.
-perfect integration of the Microsoft controller, and also very good response when linking a ps3 controller via 3rd party apps.
-no longer has slow mo, and training that was included in the GameCube release.