The most fundamental problem with OS/2 is that it wasn't designed as a multi-user OS from the start. It had some multi-user functionality but there were core architectural problems that made it impossible to move forward without a complete rewrite.
On the UI side it also had a single input queue. Which was such a stupid design decision that I can't imagine what they were thinking. Fixing that would have also required a major rewrite.
On the UI side it also had a single input queue. Which was such a stupid design decision that I can't imagine what they were thinking. Fixing that would have also required a major rewrite.