I fully understand your criticisms of Eluveitie sounding repetitive over the course of a few albums. Myself having listened to Everything Remains (As It Never Was) and Slania, I find it difficult to find any difference instrumentally between them. Never the less, I will give Helvetios a listen.
A fairly great album, somewhat tarnished by the poor value of a few songs such as Havoc or The Siege. Also, in my opinion A rose for Epona felt completely out of tune with the rest. Loved the "concept album" thingy though.
While Helvetios won't be remembered as the greatest Eluveitie album, it certainly is worth remembering. There are some great riffs and lyrics in there - not to mention this gaullish nostalgia, which i just love.