It was a pretty big success in Japan indeed and did respectable numbers in other world markets outside of the U.S. (and was eventually released in the U.S. but was DOA).

There's a few interesting variants of the hardware too, like dedicated MIDI composers, and a version that let's you do video compositing (display MSX graphics over top of video using a dedicated "transparent" color) like an early video toaster.

There's still a surprisingly active scene for it (unlike the Amstrad or Atari 8-bit machines). Nowhere near the C64, ZX, or Apple II levels.

I think one of the problems was that the architecture was dated when it started, and relied on an architecture that wasn't going to go anywhere (Z80). So building a cheap 8-bit machine at the beginning wasn't hard. And in the later years building the most powerful 8-bit machines imaginable became easy as well. But the move to bigger bit architectures was very hard. The Turbo-R spec tried, but the market had already moved on.

In Japan, other PC standards caught on and lasted longer. The NEC PC-88 line for example, was a business oriented 8-bit computer that was Z80 also. But when the market clearly needed a 16-bit upgrade, they simply moved to the 8086 line. Which as you can guess gave them a core architecture that lasted well into the 80386 days...but was not entirely IBM PC compatible.

Other Japanese PC standards like the Sharp X1 were also Z80 based. But when they jumped to 16-bit they went with the Motorola 68k architecture and produced the X68000 which also got it up through the 32-bit 68030 days. Despite being fantastic hardware (much more capable than the comparable Amiga), Sharp never released the line outside of Japan.

Well after the IBM PC standard had won the battle for PCs (with Apple hanging on), Japan still tried to produce non-PC compatible systems. Fujitsu's FM Towns is the most well known. Basically a 32-bit super desktop PC built around the 80386SX (and went up to the Pentium line) with lots of custom, Amiga like, hardware to support an a CD-ROM drive as standard. It had great graphics and audio capability for the time. The system was designed to boot to live software from CDs, so users wouldn't have to muck around in DOS or Windows to launch software. It worked great, but the fact of the matter is that most of the software on the FM Towns are just ports of PC software with small upgrades in graphics or sound. You could also boot direct to "Towns OS" in 1989 2 years before anything else could boot to an OS from an optical disk. There was a brief play to try to "consolize" the FM Towns and a variant called the "FM Towns Marty" was released which was the first 32-bit console ever released.

If you ever get a chance the FM Towns ports of LucasArts games are generally superior to the PC releases and ScummVM supports them.