Multimedia-oriented headphones come in a very wide variety these days, and the factors that you should count in when buying one are vast.
I haven't had any of the Steelseries headphones on my hands, so I can't comment on that, but I used some high-end / DJ / Studio headphones, and more or less the same rules apply.
I'm sure that there are a plethora of headphone guides out there, but I'll just share my own thoughts...
1. Considering you'll wear these headphones for prolonged periods as a gamer / multimedia user, it's very important to be comfortable - not too tight, but also not too loose. If you have the chance, consider making a test by wearing them a bit before you buy (you can test their sound too this way). I have some closed-cup Pioneer DJ5000 headphones designed to be tight to isolate from loud crowds, but I can't wear them more than 30 mins - 1 hour continuously.
2. The acoustic enclosure architecture is also very important, and you can split headphone categories by this criteria - some are closed-cup, some are open, some have a more complicated design. This has an influence on the sound response and external sound isolation (if desirable).
3. If you want to have an accurate, clear sound, take a good look at the frequency range. The human ear is capable of perceiving sounds between 15-25 Hz to 18-22 KHz, so look forward to cover this spectrum - esp. for low frequencies for games / music / movies. The response frequency is normally measured for <3 db deviation, but some companies still use 6 db or more to artificially increase the frequency response specs, so be careful at the small fiery letters when reading the specs, or call and ask for more details.
4. Other specs to take into account are the speaker diameter (mm) influencing low-frequency response, output power (W) and sound level (dB/mW) influencing the 'loudness' of the headphones - NB: high volumes should never be used - "Engineers who fry their ears, find themselves with short careers" - an old Mackie manual says.
5. Also, the cord length and jack quality are to be checked; Most high-quality are gold-plated 6.35 mm jacks for low contact impedance / high contact surface / lower oxidation problems, but for multimedia use, 3.5 mm is the most wide-spread. Choose headphones with a solid cable - very thin cables will lead to problems sooner or later.
As brands, there are many, and most have both low-end and high-end solutions, so brand is not everything. I prefer Yamaha, Technics, Pioneer, Sennheiser, and others that don't come to mind now, but that's more on the Studio / DJ side.
Hope my few points help you in making a good choice, Cheers.
Oh, and i forgot to mention - I don't believe in 5.1 headphones.
All agreed, 5.1 headphones sound more 'spacey' but the same result can be obtained using a software / hardware DSP or DST stage, or a generic SRS sandbox or similar application.
If you study the way the human ear perceives sound and its location, you'll find that binaural sound, so close to the ear, will be more than sufficient (and higher quality).
The sound location is determined by:
1. the phase difference (determine by the inter-arrive time of a certain sound) -- helps determine the horizontal position of a sound
2. close external ear reflection (the reason for which the back our ear is curled) generating secondary close reflections (another instance of the same sound, but delayed a few fractions of ms) -- helps determine the vertical position of a sound
3. amplitude difference (due to distance and diffraction)
4. harmonic content difference (due to diffraction)
A normal 5.1 audio system (home theater) takes advantage of all these factors, while a headphone system will take advantage only virtually of these factors, cause they are very close to the ear itself (the ear having a single reception system)