jd_earth,
On a whole, the Luna is a very nice unit as are all of the Galilleo units. The Luna is to a degree modular compared to the SOL and TERRA units in that it can be purchased I beleive with or without the Heart Rate Monitor or gas integration, so effecticly it can start life as a Terr and finish up as a SOL, albeit at a cost.
The good points are probably the display and the compass and, if you use (and pay for it) the 3 gas blend option if you are going to use stages at different o2 levels. The display is configurable from giving you total information overload in one screen to giving you only the essentials. When on the basic screen, the other info can be brought up at the tap of a button.
The compass is big and works in any angle. It does seem to be more tolerant to areas of high metal content compared to a normal magnetic compass (i.e. when diving around bridges or wrecks) but is a right royal pain in tha arse when you are getting close to your NDL and you want to navigate back on a bearing as the computer takes over and reverts the compass back to the Dive screen. Real bugger when you are runnng tight on bottom time and you are having an argument with it as to what screen you want to see
The Luna is a big unit so be aware that it will not stay in its pristine condition for long if you are into poking your nose into tight spots as you will no doubt to banging it on rocks or wrecks. But, it is solid and can take a fair bit of punishment. Being big, so is the display so if you are like me with aging eye sight, you can read it no prob.
Some say the Heart Rate monitor os a bit of a wank but the theory behind it in calculating nitrogent absorbtion based on respiration I think is quite neat. The Air integration (if you take the option) is the same as any other computer.
The software for logging your dives is very good, probably one of the better I have seen or used. And having said this, the dive profile is displayable on the big display on your arm.
All in all I personally think it is a great unit. Do I own one.... no I have the Terra, do I want one .... Yep.
Cheers
Rainsey