Only took me like 12 hours, but I finally got halfway through the game and picked up the electic guitar. This weapon is awesome. When you first hit attack, you whirl it off your back to get ready to play. This hits anyone nearby with the blades on it. If you move or anything, it goes on your back, so you have to stand still. Then you hit attack and start playing, this summons a swarm of bats, up to 4 swarms depending on how long you play, then release and they attack whatever you are targeting.
If you tap attack and push a certain direction, you will fall to your knees and start jaming out in a tornado of lightning and huge swarms of bats, taking down anything inside the radius.
You can get tons of powerups for this. One is called something like amp up the volume, it lets you summon bat swarms faster. Another lets you do a move similar to the Stinger (knockdown move), and another lets you do a move similar to high time (juggling move).. you can get level 2 on both of those, which lets you strum some cords afterwords, summoning bats and lighting to do additional damage. Finally, you can get Air Raid, and if you've played DMC 1, then you know what this is about. Turn into a flying devil and launch lighting bolts from your fingertips.
Swordmaster levels give additional moves. If you are level 1 swordmaster, then you can swing around the guitar like an axe. 2nd level gives you this whirlwind type attack, you spin around and hit everything around you with lighting and your guitar blades. 3rd level lets you distort your guitar for a super-powered ranged attack.