I just beat Merveil. Dual strike seems to make a lot of these early bosses and rares kind of a joke. I also got a lifesteal gem on my Reave which basically makes me even more unkillable. I've only died once when the medicine chest island unique got a lucky freeze on me while a bunch of cannibals were hitting me.
Dual Strike FTW. Enjoy it while it lasts though, because without serious damage scaling, you don't do the DPS you need to against later bosses, because they'll force you to move or die and you don't get your DS awesomeness consistently applied. A lot of uniques even in normal eat melees for breakfast. (Gravidius comes to mind.) The trap you fall into is you can Dual Strike your way through an entire horde of normals and blues, to pulp the Yellow at the center. Up until Act 3, when suddenly trash stops dying so fast, a pack of blues becomes a serious threat and you end up surrounded.
Which is why I always try to keep a ranged AoE solution on hand. For Dex classes, a bow and Poison Arrow can do a ton of AoE damage with very little work, especially if you can maintain your attack speed between gear sets. Or you can just slap Firestorm on. (Man, Firestorm. I wish the skill wasn't as good as it is, because it ends up on every one of my characters.)