I also like the 405CX.
There is a bit of a learning curve as with most technology. I like that I can choose a vast array of screen settings, ie overall pace, current pace, distance etc.
The bezel is quite finicky when wet so I don't toggle for screens or info during a run. I have the data I need during the run on the screen anyway.
I like that I can download it to both the Garmin site and to my online running log.
I haven't started using the HR monitor. I'm not sure what to do with that data yet. Perhaps I'll start just for the geekiness of it.
If you are an ultra guy the battery duration might be a problem.