If there were any lingering doubts about the "value" of the PC 350s, these are quickly extinguished when you start playing games. For starters, the microphone is simply superb. No echo, no feedback, just clean and clear audio with noise cancelling ensuring that no background noise (i.e. TVs, phones, screaming children) interferes. It makes communicating with allies and enemies alike completely painless.
And since we're on the topic of enemies, the PC350s provide just about the best audio placement and spatial awareness we've experienced. This is demonstrated very well by how much easier it is to detect Spies in Team Fortress 2 using the PC 350s, as opposed to the P166s. If one de-cloaks nearby you'll be instantly alerted, as you will if he swings his knife in your vicinity - particularly useful when playing the Sniper or Engineer classes. This applies equally to all situations and with the PC 350s you'll always quickly identify where danger is coming from, though the response is still up to you!
This prowess does come at some cost, though. To achieve this great clarity the PC 350s have a fairly strong leaning toward the mid and high end of the frequency range. Consequently bass, though present, lacks the power and punch that even the PC 166s deliver. This isn't a great problem in online multiplayer games but in single-player games, where the emphasis lies more in immersion, the bass response does mean explosions lack a level of gravitas.
It also makes the PC 350s a difficult proposition for music listening. If you listen to a lot of music that's heavy on percussion and vocals and light on bass then these will suit you very well. Clarity is excellent and the large cups create a surprisingly good spatial effect. But, dance, hip-hop/rap and other bass heavy genres don't come out as well, while guitar heavy music can sound somewhat harsh and unpleasant.
Much the same can be said where film and video watching is concerned. Dialogue clarity is superb and when used with headphone virtualisation (e.g. Dolby Headphone) the surround effect is excellent, but action scenes are still let down by the comparative lack of bass and high frequency leanings. Tweaking equaliser settings will aid bass production to an extent, but the PC 350s never quite achieve the warmth and strength that's desirable.
Finally, and this is an observation rather than a criticism, if you do use the PC 350s with on-board audio be prepared for some clearly audible distortion and interference. It's particularly noticeable when using the microphone and though your experience will depend on your PC, it should go without saying you need a decent soundcard to get the most out of the PC 350s.
Sennheiser's PC 350 PRO-Gaming Headset isn't the most versatile set you're likely to find, neither is it the best value. If, however, you want the very best headset for gaming but nothing else, and have spent a lot of money on a high-end gaming machine with a soundcard to match, you owe it to yourself to pick up a pair. They're strong, obscenely comfortable and produce a level of clarity that ensures you shouldn't miss a thing. The excuses end here.