Frameworks are interesting. In general, they're really great - they increase speed of development, often provide a good boiler plate set of styles - for greater uniform consistency throughout your site, and if they're worth their weight, include some kind of neato burrito responsive features already built in.
So whats the problem?
Most design on the internet is not timeless - for whatever reason, its not like print. Design trends become stale once they've saturated the market.
I remember the first day I saw Bootstrap and thinking to myself, "wow, this cool, I'm curious if it'll impact the value of design (i.e. if anyone can do it, are designers useless?)" but what I saw, was an explosion of bootstrap adoption. Everyone did. Now when I notice a site's design is "bootstrapped" I only make judgements:
- They probably don't have a designer
- This is ugly
- Not innovative
The judgements might not be accurate, but thats exactly what they are (judgements). When I discussed this with a co-worker (engineer), they simply said, "the more you use out of the box, the less seriously I take your site."
I remember when the Motorola Razr first came out - it was incredible, so thin, so cool. At the end of it's life cycle, it was a piece of shit that everyone and their mother owned. It's rarity of design, what made it so special & unique, was completely dead.
Frameworks often do this to styles of design (consider any popular CMS wordpress/phpnuke/joomla/drupal etc. theme). Right now "flat ui" is enormously popular, it will rise and rise, and at some point, someone will just make something that will make flat design look crappy - solely because they're innovating, they're unique, and they're creating value through innovation and standing out.
Choose your frameworks with caution, embracing the good (grids, responsive elements) - but innovate and push to stand-apart, create your own designs.