Well their first four albums are all in the same vein, so if you liked Ecliptica, odds are you'll like Silence, Winterheart's Guild and Reckoning Night too. Out of these four, Ecliptica is easily my favourite and Reckoning Night is my second favourite, so if you want some good old power metal, go with Reckoning Night.
Unia (the album from which I've chosen a song for Parama) is definitely the weirdest they've ever recorded, and it's tough to get into, but when you do, it's really rewarding because most of the songs there are complex and brilliant. Took me like six or seven years to get into this one, to be honest.
I would also recommend considering to check out The Days of Grays, which is a follow-up to Unia. It's the darkest Sonata Arctica album, and while a lot of people seem to kind of disregard it and say it's not that good, I think it's up there with their best - but that could be just because I like some sad and dark music (though it's obviously not that dark, it's only dark by SA standards).
So, if you want pure power metal, the best choice is Reckoning Night or Silence, if you want weirdness, go with Unia, if you want something darker, go with The Days of Grays. I can recommend you some tracks to check out (1-3 from each album) in PM if you're interested.