Howdy,
Well I tried a fire shugenja ratling a few weeks back. I found shugneja to be on par with sorcerers in the firepower department and in soem ways can really outshine thme in it. Now at low levels a fire shugenja will hurt because of the lack of damage spells(no magic missile!) as compared to a sorcerer but in the end will outstrip them. I got to 7th level with my rat and he was absolutely lethal. For me shugenja hold a few advantages over sorcerer, skill points and armor. That is far better than a sorcerer's familiar. The noe drawback I see for shugenja's are the lack of spells from the other elements. Also they can only choose the other element spells at a higher level. This means tha shugenja's wil lbe a bit one tracked at the start but will get to expand later on.
But in the end, shugenja's rock.