We enjoyed having a volume adjuster on the side of the headphones, but didn't really notice much of a discernible difference when turning the bass-boost switch on. It does add a sliver of richness, but it's not drastic, by any means. If you're concerned with maximizing battery life on the headphones, we'd recommend leaving the feature off.
Our experience with using the X4s to chat during gameplay was very good. Incorporating chat requires you to connect the headphones to your 360 controller via the included wired adapter. This is almost exactly the same adapter that is on the end of the Microsoft-branded headset, complete with a microphone mute switch and volume wheel. A wireless solution for chat would have been ideal, but we'd imagine this would severely compromise battery life on the headphones. While we didn't necessarily notice it in action, Turtle Beach claims the X4 contains an autoadjusting chat-volume feature to compensate for noisy gaming sessions. Regardless, there was never an issue with hearing anyone during our online play with Rainbow Six Vegas 2.
Overall, the Ear Force X4 headphones provide a great-sounding experience for playing games when using external speaks isn't an option. We'd imagine a few gamers would even prefer the X4s, regardless of the situation, as they provide accurate 5.1-channel surround-sound effects. Similarly, this is certainly a well-advised alternative for those gamers who don't have an external surround-sound system. The X4s' $200 list price is a bit steep, but with online prices closer to $180, you could think of it as an alternative to buying three mediocre games. And, when you consider that the Ear Force X4s are compatible with almost any source, they may be the only wireless headphones you'll need for a while.