The Halo series of soundtracks - and the original Halo: Combat Evolved soundtrack - are modern classics of the videogame OST genre.
This Anniversary edition builds on the original soundtrack and - by golly - it sounds great. Certainly, the music is much richer, and contains far more depth, thanks to the full orchestra behind the scenes.
However, what was utterly astonishing as an original 1-CD collection of tracks has been turned into "merely brilliant" with this re-release and re-mastering onto 2-CDs. The additional space has been filled with a lot of the more ambient music, and the collection as a whole loses focus and - at times - almost becomes background music. Fine for the videogame, less so when you're trying to appreciate the soundtrack in isolation.
If you're a Halo fan, or simply adored the original Halo soundtrack - then this CD is a no-brainer must-purchase. You'll appreciate the extra depth and clarity that have been lovingly lavished onto the original tracks. However, the new additions are somewhat more questionable - but then, you could always just skip these! :)