Insomnium's weakest point is definitely the vocals but they're not bad. The clean vocals they use are bad, but the growling does the job. Either way, the melodies are so good (usually, except for the 2014 album...one of their weakest) it doesn't matter. Just listen to Equivalence + Down with the Sun. That is some powerful riffing going on. Also, Against The Stream has great, melancholic riff work. I like the happy sounding stuff if it's done well, like early IF and Skyfire, but I usually prefer the sad, sorrowful melodies of Wolfheart, Insomnium, Omnium Gatherum, Hypocrisy, etc. I find Amon Amarth to be good but over rated. I don't hear any progression in their albums.