For me power metal is powerful when it slows down and has some crunchy riffs and time changes etc..... rather than being some sort of double kick marathon ,so I like albums where this tends to happen a lot. That's why I like Nemesis (and most of the recent albums) along with tracks like Kiss of Judas ,Uncertainty, We Hold The Key etc...
My top 4 would be (no particular order) Nemesis, Elysium , Episode and Fourth Dimension. I have a soft spot for Fourth Dimension as it was my first of theirs (bought around the time of release). We Hold The Key really blew me away at the time and it remains one of the hugest guitar/key sounds I've heard ,despite perhaps sounding a touch dated now.