When comparing Gnome Builder vs Code::Blocks, the Slant community recommends Code::Blocks for most people. In the question“What are the best IDEs for C++ on UNIX-like systems?” Code::Blocks is ranked 4th while Gnome Builder is ranked 17th.
Ranked in these QuestionsQuestion Ranking
Pros

Pro Great language support (for linux based projects)
Python, C, Java, Javascript, Go, Vala, C++, and many more.

Pro Integrates nicely into the GNOME Desktop Environment
Client-side decorations, good use of widgets.

Pro Lovely find and replace tool with great REGEX support
Shows a live feedback of what matches the pattern/criteria entered.

Pro Terminal built in
Fully featured terminal is packaged.

Pro Autocomplete
Fast autocomplete.

Pro Supports versioning (git)
Shows diff indication and has branch integration too.
Pro Integrated debugging

Pro Integrated system-wide profiler for improving software performance

Pro Templating
Good templates available to build applications, even to build gnome applications.

Pro Tiling Editor capability
Supports Tiling.
Pro Extendable through plugins
Pro Lightweight
Pro Easy to use
Pro Simple Library import
Cons
Con No project management
Because it is still in early development there are little project management functionalities.
Con Hard to set up
Con Not very feature rich
By default it's not much more than "What if Gedit had a compiler and a terminal built in?" (or: "What if Notepad had colour coding, auto indents, file structure, a compiler and a terminal built in?")
There are far more professional IDEs out there. This one is much too basic for any efficient use.
Con Slow navigation using mouse
In most IDE's, you can "goto declaration"/"implementation" by holding CTRL and left-clicking on an identifier or include directory. This does not work in Code::Blocks no matter what settings you have. Right-clicking will bring-up a menu that includes these "goto" options, but it's not instant and you'll be slowed down immensely depending on how often you have to do it.
Con Can get quite slow and doesn't look all that good
Con Setting up dark theme requires using system's own gui toolkit

Con Lots of functionality is encountered only in plugins
You can't change keyboard shortcuts, neither share themes with vanilla codeblocks, for example.
