A bunch to reply to here, so I'll see how I go.
@Cornfedhick, I'd say that Somewhere far Beyond is the first true BG Power metal album. Tales from the Twilight World was definitely more melodic than the first 2 albums but for every Lord of the Rings there's a Goodbye My Friend and overall I feel the album is still quite heavy. I'd probably classify the album as a hybrid of speed and power metal. Although to be fair Blind guardian overall are definitely heavier than your standard power metal band. Additionally, I do like your comparison of Valhalla with Fear of the Dark in terms of being the singalong type, although there is one thing slighty off here, Valhalla is a brilliant song whereas Fear of the Dark is not. <ducks from the rotten tomatoes>
My favourite album would definitely be Tales From the Twilight World, the blend between the speed and power metal elements is unbeatable for me at least. Then it would be Nightfall in Middle Earth 2nd, and Somewhere Far Beyond and Follow the Blind joint 3rd. One thought I do have about Nightfall is that I think they could have done a double album with it, instead of having 20-40 second interlude pieces everywhere, although of course we don't actually know if they would have enough good material for something like that.
Like Night Prowler, I'm not a huge fan of the over the top overdubbing featured heavily on some of the later albums. Additionally, for all the pure ballads that Blind Guardian have, the only one that has really grabbed me is Blood Tears. So I would say that I prefer the heavier side to the band, especially looking at my favourite BG songs. My personal top 10 is dominated by stuff like Majesty, Valhalla, Mirror Mirror and the like. Speaking of Majesty I am slightly disappointed by the fact that it hasn't come up in the discussion at all, although it is a different beast to Valhalla. Majesty has a somewhat repetitive song structure especially for it's length but makes up for that with brilliant riffing and solos, engaging lyrics and I do really love how Hansi delivers them here.
However, I feel that the most underrated song of all is the instrumental from Follow the Blind, Beyond the Ice. This song has a ton of great riffs in it, kickass solos and plenty of changes throughout the song so you don't really know what's coming next. In fact it reminds me alot of a couple of Maiden's instrumentals (Transylvania and Genghis Khan).