If you read overseas forums you're probably aware of the black crush issue with season 8. If not, you'll be wondering WTF happened when you slip in the first season 8 disc - no shadow detail and most scenes unwatchable unless filmed outdoors. Seems someone stuffed up bad with the video mastering and no-one caught it before signing off.
Some more details here, along with contact details and a pro forma for replacement discs from Fox (no, not Mulder!). The blu-ray screenshots they've posted like like they were done with a very bright display - much worse on my X500.
For those planning on buying the boxset or individual seasons, I haven't seen any news of revised versions in the wild yet, so expect to have to chase replacement discs.
A few blu-ray.com members in the US have reported receiving corrected replacement discs, but latest news is that Fox is out of stock at present.