Although I think the next installment in the Fast & Furious franchise will be different, it will be just as good. The truth of the matter is that these kind of movies are able to succeed no matter who stars in them. Because as we all know, it's pretty much about the cars, the girls and the music.
Movie franchises seldom rely on the strength of individual actors. Rather, they rely on a concept that continuously evolves. This is evidence in the fact that very few franchises every win acting awards. With this in mind, it is completely reasonable to believe that Fast & Furious 7 will be as good as its predecessors.
I think that the directors of the movie will be able to find a suitable replacement for Paul Walker, I think the film will be emotionally charged with all the actors giving their best performances due to the respect they wish to pay for Paul Walkers death, I think the movie will be very popular and well put together.
I do not think that Fast & Furious 7 will be quite as good without Paul Walker. Although I think that it will still be very good. Paul Walker was a charismatic actor and he added a lot to the movie. I think the other actors will have a hard time making up for him being gone.
I don't think that the Fast & Furious movies were good to begin with. I know that there were some die hard fans of Paul Walker, but from what I have seen, the Fast & Furious movies were hastily thrown together action movies with focus on the special effects and stunts. I don't think that the actor would ultimately be missed as much as the fans might initially think.