Noteworthy differences:
The click has rising and falling edge contacts that replace the inline one-shot instructions (OSR or ONS)
The first scan bit in a click does not fire when the PLC enters run mode from program mode, only when it powers up. It should be called a power-up first scan bit.
MSG instructions are replaced with SEND or RECEIVE instructions and those will happen repeatedly as long as the rung is true. If you put a rising edge contact ahead of them in an attempt to mimic SLC/Micrologix behavior, you may not get consistent results.
None of the data values can be seen or edited offline in a Click.
The Click uses one MATH instruction for all math operations. It is much like the CPT in RSLogix.
The Click uses the COPY instruction in place of MOV and COP instructions in RSLogix, but the behavior is different in certain situations, like trying to copy the bit pattern of a Float into two consecutive integers.
There are probably other important things I am not thinking of right now.
I have quite a few Clicks doing some relatively complicated controls and communications and I generally like them. If they'd add trending and make the communications instruction behavior more like the SLC/Micrologix, that would be nice.
If they'd do that and add serial DF1 radio modem protocol, I might never buy another Micrologix PLC.
One thing they do that a SLC can't is store all the comments and data views in the PLC. Their PID implementation performs better than a SLC/Micro and includes Autotune that worked perfectly the one time I tried it. Interestingly, you can view a Trend of a Click PID, but not just any old tags of your choosing.