If you're looking to build an essential collection, these five albums are widely considered the pillars of his career: The Complete Frank Zappa Project/Object Series - Part I
Conclusion
Format: RAR 5.0 (solid archive, recovery record 5%)
Total size: ~88 GB (FLAC) | ~28 GB (MP3)
Split archives: 750MB parts for easy download
The Early Years and Experimentation
Many of these are available on Zappateers (lossless trading site) or via Soulseek.
As the decade progressed, Zappa's music became increasingly complex and jazz-oriented. Shark Sandwich (1974) and One Size Fits All (1975) demonstrated his mastery of jazz-rock fusion, featuring intricate instrumental passages and virtuosic solos.