To say that I've waited for Kriemhild for a long time to finally become an official Servant would be an understatement, especially after some fanartists' take on her, like Suzaku Darknight's, which is particularly good.
Now, while I definitely think Kriemhild should have been an Avenger, I can do with her being a Berserker. I like her pale skin and hair design with two moles under an eye as well as her various outfits, be it her third one's armored dress or her second one's uniform (that makes me think of GuP's Kuromorimine), but there's no denying that she looks good in that black gothic dress. Good thing she's not a grief-stricken weeping widow, but a vengeful one.
Also, while I'd have prefered her version of Balmung to be something more simple, I totally dig Otsutsugu's design for the sword, halfway between Stormbringer and Soul Edge.
All in all, Kriemhild is definitely a good addition to the roster, and I couldn't be happier that my man Siegfried can finally be reunited with his wife.
Now, while I definitely think Kriemhild should have been an Avenger, I can do with her being a Berserker.
This is actually addressed in lore, since her revenge was based on a lie (since she didn't know Siegfried killed himself and wrongly assumed Hagan murdered him) she lacks the one criteria needed to be an Avenger (That she believed her vengeance to be the 100% truth) and instead is a Berserker due to the fact her plot eventually cost her everything including her sanity,