Yesss! Being able to drop a few buttons, code a few lines, and compile, and get a statically compiled binary / exe file with native GUI, on all the three desktop platform (without any code change between them!) is just mind blowing if you tried any other GUI builder. This is how GUIs should be made. Period. :)
It's amazing if you're into Pascal. You don't really need anything else. But other languages advanced further these days.
That aside, one thing that I like about FP is their text-mode IDE. They basically copied Borland's original Turbo Pascal (circa 7.0) IDE for DOS. Except this one runs on Linux etc. And, of course, has a lot more features. There's something about that TUI goodness that is hard to capture in modern GUI IDEs - and then it's also blazing fast (you think Sublime is fast? ha).
It compiles to just about any platform you can come up with.
You can build a GUI app for any platform and backend without having to change a lot of code.
Builds to Linux, ARM/x86/x64, macOS, iOS, android, Windows, freeBSD and I'm sure I'm missing a few.
It actualy surpassed Delphi in some ways. You can develop native programs on non x86 platforms. The IDE and compiler installs and runs fine on the Raspberry/Nano/Orange PI boards, and others, so if you want to write a GUI to view sensors and actuators status, or maybe a display for a homemade KSP controller, the tools are there already. Free both as in beer and speech.
I currently consider using it instead of C++/Qt for a major desktop application, but I'm still undecided. Lack of good Emacs support is a major downside but the same is probably true for Qt (haven't checked yet).
Still I feel that going with Qt is more future proof.
If you haven't tried Lazarus/FreePascal, you're missing out. It's really amazing, and it's truly free.