The only metal festivals I have been to are Hammerfest (Wales) & Bloodstock, besides smaller underground ones.
The first few years of Hammerfest were excellent, attended every year from when it started in 2009 until 2014. If anyone went during 2009-2012 they would know of the old location, which to my opinion had a better vibe. I Haven't gone recently due to decline in production/promotion and escalated prices, I felt it was time to break tradition and save some pennies. Bloodstock on the other hand seems to get greater every year. I was present in 2010, '11, '12 & more recently in 2016.
In 2012, I accidentally left a red bag at Bloodstock containing a light blue kutte and lots of loose patches. On the jacket there were a few badly sewn patches; a large Windir logo back-patch, Tankard - Alien patch, Finntroll patch to the bottom center. There was also a yellow/blue In Flames raglan inside the bag, depicting the logo in Carlsberg font with the slogan "Probably the best band in the world". It resembled a Swedish jersey and I had cut the sleeves short. Hopefully some items will boomerang one day, I think I'd took some photos before I lost it so I will upload them when I get round to it.
A patch I miss (among many others) was an unofficial Amon Amarth patch, It had an orange border, black background & the font was red with yellow stitching around the outside. If you know about any of the items I mentioned please return & I will reward with money or maybe swap some patches with you.
As for future festivals, I hope to venture to Wacken, Hellfest, Brutal Assault, Obscene Extreme & if I'm really lucky 20,000 Tons of Metal.