Shadow, you would do well to use binaural recordings as a test, as well as normal gameplay.
Binaural reordings are created with microphones situated inside a model of a human head, and they're designed to be played on headphones. The cheesy recordings have sounds that circle the head, and those sounds give you a very good sense of position and relative volume levels when sounds are "in front of" or "behind" your head, rather than just off to the sides. There are a number of stickied threads on these forums with links to excellent, and free, binaural recordings.
I think you'd do well with the 555s, by the way. I'm not a gamer at all, but I greatly appreciate effective soundstage in music, and both rely on a headphone's ability to interpret directional cues. The 555s move the physical transducer away from your ear, which more closely resembles the positioning of actual speakers. I moved on to other headphones for music, but for movies and gaming those can definitely be the end of the line.
Should you, at some time down the road, desire to hear your music in higher fidelity than you currently do, you should consider an amp. This step should probably be taken after you've upgraded your soundcard (or bought an external a/d converter) and upgraded the bit rate of your source files. Your soundcard uses so-so opamps, and those draw their power from a noisy source (your computer's power supply). An external amp uses a dedicated power supply and higher quality components. If you're not deterred by your lackluster welcoming committee here (and willing to stop using audiophile as a term of derision in an audiophile community) you'll find a lot of good information here about cost-effective DIY amps, and/or inexpensive off the shelf amps.
Be prepared to invest upwards of $100 per component to get a noticeable increase in sound-quality. That's just the rule around these parts. Other people revise that estimate upwards, sometimes as high as 7 or 8 hundred dollars. For me, if it's less than $100 it's not as good as what I've already got.
Welcome to head-fi... soz.