Below is what you need to know. Once you understand and know the difference, you pretty much have main/solid idea about cams.
1. Resolution. 4K, 2K, 1080, 720.
2. Frame rate. 60, 30, 24(!)
3. Progressive vs. Interlaced
4. Codec. AVCHD, H.264, MPEG-4, MPEG-2.
5. Encoder performance/algorithm. B-frame, CABAC.