I also really like the Luna (my wife has it, I have the Sol).
I would agree with Dr. Lecter that for more complex dives (way beyond "noob" stage) the Luna requires more pre-dive set-up than something like a Petrel, but during actual dive operation, once properly set up, I find it intuitive, VERY well laid out in terms of the information, and easy to read due to the size. I also like the gas integration for the data I learn from it (but you should always dive with a back-up spg). Its electronic compass is the best compass bar none that I have ever used (including my beloved Suunto SK7).
The Luna is also highly configurable with multiple possible alerts/alarms, and multiple possible display layouts. This can add complexity to the set-up depending on how many of these you want or don't want (you can turn many of them off, as well). However, you can go with the standard settings and be just fine. As you get more experience, you can fine-tune the settings to your dive preferences.
I sum, like the others, I would say good choice that will last you a very long time.
Oh, read the manual read the manual read the manual!
You're the same noob that got the S600/MK25, so you are doing pretty well, I would say. That reg is a top breather (wife has it, I have Apeks and I think hers breathes a little better).