A lot of people, including the creator, believed the dub was better than the original voice acting (sorry, no source for this). Regardless of what they aim for with the voices in this movie, they will fall short, I'm sure. Specifically Keanu. This has already been said, but his generally monotone, almost lifeless voice is a far stretch from either version of Spike. I guess I will miss Spike's signature hair, as well, but that's not really going to be important when you consider all the other major attributes that will almost assuredly be ruined.
Also, Spike d---err...woops, little too much 4chan.