Intel iAPX 286
The Intel iAPX286 (often given as 80286 or i286 or some variant) was the second generation 8088/8086 CPU. The 286 was noted for being more efficent then the prior parts, so at the same clock speed it was slightly faster.
There was however two major flaws with the 286. The first being that all the memory was divided in 64KB segments. With the ever growing popularity of the Motorola 68K CPU's flat address space, this was a major problem, as it hampered the design & porting of large programs. Also the 286 had no method of switching the CPU from protected mode to real mode.
It was Gordon Letwin of Microsoft who found a way using a triple fault to soft reset the 286 into real mode, however it could take nearly 1 second, making switching from protected to real not feasible to be done often. However this is what made OS/2 feasible as now it could offer limited MS-DOS compatibility.
The 286 was seen by the software business as being a rather disapointing CPU. Intel listened, and its next chip, the 386, corrected all the issues people had with the 286.
In my opinion the 80286 CPU held the industry back some 10 years, as most people that owned 286 CPU's never hard more then 1MB of ram, and this led to so many things at the time trying to cater to the 286 protected mode, instead of taking advantage of the 386.