LOL
i know all their albums and i am guitar player since 15 years and played in several rock bands ...
k lets go for a more complete explanation ;)
iron maiden is a part of well known NWOBHM (New Wave of British Heavy Metal) in heighties with a lot of other groups. iron had not crafted this music movement, this is just a continuity. When you listen iron maiden, you clearly listen their influences: judas priest, kiss, saxon, deff lepard, venom ...
thats sound good, but iron stay in NWOBHM credo : speed guitar, clean melody, clean drums, loss of blues influence, basic structure of songs (chorus-verse-chorus-verse...)
iron purposes, lyrics and graphics are based on fight good vs evil, fantasy, occult, demon and blabla; thats means that for me it s for buble face teenagers which like daaaark speaking; but btw lyrics means nothing that just "we are so daaaark^^"
yeah that for kids ^^ cause lyrics are not mature
iron never bring heavy metal lol; listen led zep, black sabbath, deep purple, ACDC, Cooper which played and crafted heavy metal well before iron maiden !
now metallica
metallica has taken influence and created a very unique song movement. influensed by heavy metal but also rageous guys of punk rock, metallica crafted load rock. metallica is in the "big four of trash" (with anthras, megadeth and slayer).
metallica build load songs with complex structure (listen ride the lightining, justice for all and master of pupets...), social and mature lyrics, without compromize
last points: nirvana, rage against the machine, sonic youth and other good rock bands claims influence of mettalica and its wild music for their works. they dont care about iron maiden and its halloween lyrics and immature evocations :)
btw as i said in my first post: i like metallica and iron maiden both but recognize that they dont play in the same level ^^