There's nothing wrong with making it look more... beastly. Heck, SSJ Oozaru is as beastly as it gets. In fact, on it's own I have no problem with SSJ4. However, coupled next to the other SSJ forms, well let's see.
SSJ1
First form we see. Hair becomes blonde, hair goes up, and eyes turn green. This look is commonly associated with DBZ nowm though ironically they were the second to use it.
SSJ2
Hair becomes more refined/spikier. Eyes become more tealish. Hair is still yellow and resembles the first form
Ascended Saiyan aka USSJ
Muscles bulk up. That seems to be it. Still resembles SSJ1.
USSJ2
Hair becomes super pointy like it can prick you. Muscles become steroided past Brock Lesnar levels. However speed is lost due to the size of this form. Still resembles SSJ1 form aswell as the other forms, though.
SSJ3
The form Goku and Gotenks manage by training outside of earth's dimension.
The hair goes to medusa levels. The eye brows dissapear. Hair is still yellow. Eyes still greenish.
Golden Oozaru
A feral version of the SSJ forms. A giant feral version. You become a giant ape-wolf with golden fur. However the eyes become red, though it still resembles the other SSJ forms.
Now for the grand finale--
SSJ4 a.k.a "WTF?! Who thought of this?!"
Scrolling down through the list, it becomes quite obvious. One of these things do not belong. It's like looking in the Jughead digest books and spotting the odd things in the pictures. I mean seriously, how do you go from SSJ1, to 2, to 3, to SuperFanfic4.
First off, the fur is red!!! Freaking red! Where did this come from?! Why is it red?! After all these transformation, why red all of a sudden?! It makes no sense. It's like after watching Naruto's red chakra'd fox tailed form transformations(0-4), he suddenly transforms int ao 9tailed Kyubi which is pink chakra'd with blue hair. Yeah.
That's another thing. The hair is black or I'm guessing it never changes. So after 7 transformations (I'm counting LSSJ) where the hair is a prominent part of appearance and does change, in this form it does not. It just gets a little messy. Yeah, pillow hair. Look out bad guys, Goku's here to save the day, and he's got PILLOW HAIR. Then to add further insult to the other forms not only are the eyes not greenish, but they are a completely different color depending on who transformed. In fact, the entire transformation varies person to person, unlike previous forms. Gogeta, Goku, and Vegeta all have different colors of fur, eyes, and hair styles when in Superinconsistent4 mode. It's like someones bad fan fic made it into the DBZ mythos and is an insult to Akira Toriyama's works.
Not to mention it's the weakest form ever. You might aswell not transform into it.
http://www.youtube.com/watch?v=kApU-3s-6h0
end rant/
Sorry bout that. My anger for GT burns as strong as ever.
As for fusion, I'm not saying that can't do it, but it would never come out right, imo. There are somethings that can be left out of movies, but still have it work. Take Spider-man's web-shooters for instance.