The speaker can be startlingly loud depending on the media's volume but I haven't played much music through it to comment on quality (bass vs treble). Games don't lag unless they're system intensive and something else intensive happens at the same time, such as someone deciding to chain message you. I haven't had much issue with system lag outside of the "I just woke up/booted up and you're touching stuff too fast" issue all electronics hate.
Samsung Galaxy S® 4 MJA Rooted with CF Auto-Root Tutorial
HTC EVO Design 4G™ v4.0.3 Bootloader Unlocked & Rooted with HTC SuperTool v3
If it ain't broke, use a sledge hammer.