First off, which Version? V2.3 or V3.0?
CoDeSys V3.0 has moved very heavily in the IT direction and has a pretty high learning curve - which is probably why, although it's been on the market for a few years, the manufacturer take-up has been very slow up to now.
V2.3 is a lot easier - pure IEC. For me the main plus point is also its biggest negative - ST can be easily viewed on line, unfortunately this seems to lead to a lot of people (particularly young engineers just out of uni) programming everything in ST, which is not ideal for debugging or troubleshooting. This is probably not helped by the fact that the Function Block programming is definitely a bit wierd. When you're new to it it's not always intuitively obvious where you need to click to add a new in- or output, this isn't helped by the fact that you can get the feeling that you have to get the mouse on exactly the correct pixel to get the required effect - not easy on a full HD screen. I must admit I also don't find the FB representaion as pleasant to look at, particularly on line, as the Siemens version.
That said, the SW itself is solid and in general easy to use. The biggest challenge for newcomers is getting used to the "target" system by which the program is mapped to the desired HW - over 300 companies (290 of which probably nobody's ever heard of!) use CoDeSys for their PLCs. This means you can develop a programme and then use cheaper HW for a relatively undemanding environment and take the same programme into a harsh environment using the (more expensive) hardware from a completely different manufacturer, without having to change one line in your programme.
