Pros and Cons of Bootstrap

Pros

• Works in all modern browsers
• Normalizes many little CSS annoyances
• Lightweight
• Customizable
• Encourages use of LESS CSS (http://lesscss.org)
• Gives consistency
• Many starter templates available
• Integrated with jQuery
• Comes with some jQuery plugins
• Some jQuery plugins now offer Bootstrap theming

Cons

• Less originality
• Limited jQuery plugins. Certainly, you can integrate your own; find other 3rd party controls, etc. But out of the box, you are missing the heavy-hitters, like grids, tree views, drag and drop, etc.
• Weak for complex data entry forms
• Naming conventions and semantics are mediocre. Example: using the <i> tag for icons. Class names like "pull-right".
• It's very customizable, but inevitably many sites start looking alike (just like WordPress—consider how many blog sites look the same).