I actually wrote a long review of this lens for my personal site: Canon EF-S 55-250 mm f/4-5.6 IS STM – Initial Thoughts and Samples
To make a long story short, my conclusion is:
In one sentence - This lens is sharp. Here are two of the sample images of a hydrangea:
Like I said - Sharp.
Read the full article for more lens details and plenty of sample images.
**Note my number ratings are relative to this lens' performance for its cost. It would certainly be rated differently if compared to L-caliber lenses. However, in isolation, based on its price, I would rate it as listed above.