A superzoom like that will be the jack of many trades, master of none. If you are used to the sharpness of the prime, you may be seriously disappointed with the softness of a superzoom. My experience is limited to the 18-200 style lenses, but beyond basic sharpness, consider:

1. You are used to 50 mm f/1.8. You now want to have a starting aperture of f/3.5 (and even then, only at the widest setting). At that aperture, the zoom will be weak, and only by stopping down to something like f/6.3 or f/8 will you get quality close to what you're used to. That will make your entire shooting style different, since there will be much more light required to take the shot.

2. Composition with the 50mm is much more locked. With the zoom, angle of view becomes another portion of the equation you have to take into consideration when shooting. That may slow you down.

3. This essay was very informative on my style: Telephoto is for cowards.. That's a style decision. so if you disagree, by all means. But as a result of that, I have no lens longer than 85mm, and have not really found myself limited. That 85mm is an f/1.8 prime, and I love it.