MP3 and other lossy formats (e.g. AAC, M4A, Ogg, WMA, etc) will certainly sound different from the Redbook source even at high bitrates (320 kbps). While the MP3 encoding won't necessarily sound bad, it isn't the same as source and you should be able to hear the difference. The benefit of these types of encoding is a significant savings in file size (3-4x) while still retaining a reasonable image of the music. You'll need to decide for yourself whether or not the fidelity provided is acceptable.
FLAC and other lossless formats (e.g. ALAC, WMA Lossless, APE, etc) will encode/decode the material from/to the original WAV source precisely. No change in the sound should be heard using these formats. These formats will typically provide between 1.5x and 2x savings in file size, and as such are less space efficient than MP3, but will provide perfect fidelity.
FLAC and other lossless formats (e.g. ALAC, WMA Lossless, APE, etc) will encode/decode the material from/to the original WAV source precisely. No change in the sound should be heard using these formats. These formats will typically provide between 1.5x and 2x savings in file size, and as such are less space efficient than MP3, but will provide perfect fidelity.