These speakers are a lot smaller than I thought they would be as shown on the product image. Still, they pack high quality sound and the bass is good, despite the subwoofer being almost half the size of my last one. My one huge complaint though - these are surround sound speakers Logitech - why are the cables so short! I'm unable to mount the rear the satellites anywhere - currently with the sub/amp under my desk, the maximum distance the rear cables will reach is about 6 ft behind me, and the satellites on my desk have no further slack on the cables either. Really, the cables were quite a big disappointment as it severely limits where I can put the speakers. I don't think having the rear satellites sitting on the floor partially obscured is what these speakers were designed for. The cables seem to be some kind of RCA plug and are hardwired into the satellites, so I don't know whether it's possible to try and extend them.
Besides the cables, everything else is great. The default bass level was way too high for my liking, it took a fair bit of playing around to find a good spot where it wasn't too boomy. The matrix mode works somewhat well, although I'll probably be leaving it off since having to adjust it constantly is not really worth it. For those like me who were somewhat worried that matrix mode could only be set to "Gaming" or "Music", the button is a push-button that toggles between None, Gaming and Music, it's not a sliding switch as the pictures may make it seem.
Overall these speakers are excellent value for money - sure they won't go as loud as some of the higher end models, but they are perfectly loud enough for movies, music and games. I would not hesitate to give these 5 stars if it weren't for the issue with the cables. If you're looking for compact 5.1 system, you won't get much better value than the G51.
Update (2007-11-16): I purchased some 25ft RCA F/M cables for the rear satellites and they have much better positioning now. One additional issue I have noticed is whenever the system is powered on and not muted, the subwoofer driver is vibrating and causing a very low but discernible hum that is audible over my system noise. Raising or lowering the volume has no effect on the loudness, and the hum only stops 2-3 seconds after muting or immediately on power off, which leads me to believe it's some internal component causing it and not noisy output from the sound card or interference. We do get slightly higher than usual utility voltage, so it could be something that goes away if you have clean 120v power.
Update (2009-11-21): System died one month after warranty expired. Control pod still gets power but woofer and speakers are lifeless.