I am stoked for Retaliation obviously, and the inclusion of the Volus while odd will not detracted Dom the trailer and Harbinger's awesomeness. I will adopt a wait and see approach with these characters.
Personally I don't feel the Volus should have been included for obvious lore reason, and also because it opens a whole can of worms in regards to what can be added to multiplayer. It won't be long before people will be saying that Prothians, and Hanar should be added because the Volus were added.
But I am not up in arms and calling Bioware "stupid idiots" for wanting to include them. I have faith that Bioware will have a valid, reasonable, and non-lore breaking reason for the Volus to be included.
Case in point: When the Phantom, Kia Leng, and the Slayer, and Shadow were announced my first reaction was "Freaking SPACE NINJAS!? Mass Effect shouldn't have, and never alluded to having Sword wielding Ninjas!" But Bioware delved into detail about mono-molecular blades and about how in a world of Kinetic Shields a blade (omni or sword) made sense to be able to bypass shielding and armor. So swords and omni blades make sense lore-wise; I still subconsciously roll my eyes when the SPACE NINJA flips across the screen, but it makes sense.
As long as the Volus can be explained I can accept them being added to multiplayer; I would have preferred a more "combat ready" race like additional Salarians or Geth but I can deal with them.
However if the entire Volus lineup is just an extension of the "I AM A BIOTIC GOD!" meme then I would have a problem. If the Volus class is nothing more than a running gag that detracts from the overall atmosphere of multiplayer then I would be upset, and want to know why the Volus wasted valuable resources just for a couple of lolz.
TL; DR version: I am going to wait and see what the Volus bring to the table before I decry there inclusion. As long as the Volus classes are explained by Bioware, and are not a complete joke class I have no problem with them.