OS/2 did offer a lot of value beyond just running Windows software. The WPS (Workplace Shell) is to this day one of the better desktop UIs. It brought a lot of the classic Macintosh feel to the PC world and improved upon it. Where Windows only vaguely looked like a Macintosh, OS/2 had things like a spatial filer so it felt a lot more like a Macintosh on steroids. It had neat ideas like "template files" and a bunch of other stuff I can't even remember.
On the non-GUI front it had a better command processor, CMD.EXE, which is a precursor to the Windows NT one. It had an actually decent scripting language (REXX). It had a better filesystem (HPFS).
It was also incredibly good at running DOS games of the era, while comfortably multitasking in the background, including serial port and network usage. You could be downloading something while fragging some demons in Doom. You could also pause the game at any time and switch back to the desktop, then go back and resume.
The thing that was different between OS/2 and Linux + WINE is the engineering approach. IBM had a license to use actual DOS and Windows code, at least until they cancelled the JDA (Joint Development Agreement) contract with Microsoft in 1990. Even after they cancelled, they still had rights to everything from before, which included Windows 3.0.
In order to avoid having to pay Microsoft a royalty on the Windows portions of OS/2, which they had to pass along in the retail price, they even released a variant of OS/2 version 2.1 called "OS/2 for Windows" which took your existing Windows 3.x, the one that you almost certainly already paid for as part of your computer, and binary patched it to work under OS/2. There was some grousing when Windows 3.11 came out and broke it, but IBM issued a patch.
So, in essence, they were able to market OS/2 less like a replacement OS, and more like a utility program you added on to your existing system to make it behave better. Kind of like hey, you just dropped $2000-$3000 or more on a new system, what'a another $129 to make it really sing.
And because it leveraged the fact that you already paid for Windows when you bought the computer, compatibility was top-notch: it was actually running real Windows.
In my opinion as a user at the time, what killed it was the move to Win32 software which OS/2 couldn't run but Windows 95 could. Once computers started regularly coming with enough RAM to run Windows NT 4, the nice things about OS/2 just weren't enough to justify the inability to run basically every new software package.
