I don't want to appear as a SteelSeries-hater, but I've had very bad experiences with some of their products.
However, it should also be said that SteelSeries produces mousepads of top quality and I've read quite a lot of good reviews on their keyboards, particularly the 6Gv2. The Siberia v2 is also a splendid headset and I guess that's as far as I can go.
The only thing I'd say is "lacking" in SteelSeries products, especially when speaking about headphones(5Hv2 anyone?) or mice, it's durability. I hope they can work on the durability of their products and less on marketing, and I'm sure they'll win many more buyers as well as positive reviews.