Hi. I'm Ken and I'm addicted to golf.
I have a G6 and have used it for about 8 rounds. The reader's digest version is that it's great for helping you manage your game around the golf course. It gets it done for entering and reviewing scores. And it sucks big time when it comes to stats.
If you don't care about stats and it's in your price range my unqualified recommendation is to buy it. It would be hard to find anything better for managing your game on the course.
If you really care about stats, in-round and aggregate, forget it. It's not going to help you at all.
So now that that's done, let's address the folks who think it's a troll with such strong opinions on a first post and then get on with a more comprehensive review....
In fairness, I need to issue a wind warning.

The following is pretty long. I hope it's useful to some.
First, I have read the entire thread.
Second, I'm a veteran of electronic media. I've been using online fora of various kinds since Usenet and FidoNet. For those too young to recognize them, that's early 1980's. I recognize that not all forums think it's the best etiquette to share strong opinions on a first post. However, I don't know what else I could have posted to waste half a dozen posts just to pump my credibility. So I figured I would just jump in with both feet. And hope they don't end up in my mouth.
Third, i have a few years experience using golf GPS range finders. I started using the Intelligolf app on my Garmin iQue (integrated PalmOS and GPS) in 2005. I continued to use Intelligolf on my Palm T/X and Palm Centro (with a Garmin Bluetooth GPS10x) until I got the Approach G6.
Along the way I have used the iGolf (Bushnell) Neo for just over a season. I've used my brother's Sky Caddie a couple of times. And I have been playing with various golf apps on my Android phone for the past couple of months, with varying degrees of unhappiness. FreeCaddy is the one currently installed on the phone but it hasn't been used since I got the G6 and I really don't miss it.
The one I miss is Intelligolf. I hope they do it for Android some day. The interface is getting a little old but it does everything you could ever ask of a golf program. The best part is that it includes a PC app so you can do all your post-game/post-season analysis on the PC rather than squinting to do anything useful on a small screen.
I'm a senior whose eyesight is reaching the point where I can hit the ball farther than I can see. Even with a 3 hybrid on a good day! But I still walk and carry my clubs (Sun Mountain 3.5 carry bag) for three or four rounds a week.
Against that background I can say that the Approach G6 is a stellar device for on-course use. It gets a location lock really quickly. As soon as you hit the PLAY button it gives you a list of the nearest courses. The one at the top of the list will be the one at which you are about to step on the first tee.
It took me a couple of holes to get used to navigating between the two main on-course display screens and back and forth to the score screen and the shot distance measurement screen. It took a little longer to figure out how to end a round. It's not the greatest interface, but compared to most of the Android apps it's not bad.
As a couple of folks have already pointed out, the touch screen is a little ... well, .... touchy. Mostly it hasn't been an issue for me. But I learned quickly that when I want to measure how far I just hit a shot I should just carry it in my hand, not toss it back in my bag or stuff it in my pocket. The odds of the measurement screen not being reset to 0 are just about 0 unless you carry it so nothing can touch the screen. It really needs a standby condition (e.g. GPS is still alive but the screen is turned off until you want to look at it again).
Once you get the navigation figured out and get back to focusing on your game it's a dream to use. It gives a relatively accurate overhead view of the hole you are playing, including the primary hazards (e.g. bunkers, water features, etc.). Of course, just like any halfway decent GPS, it gives you the measurements to the front/middle/back of the green. All pretty hohum for any useful GPS device or smartphone app.
Where it really shines is when you really need the help. That is, those (hopefully rare) occasions when you have managed to somehow stray from the fairway and need guidance to get back to a visible or known position. A simple tap anywhere on the hole display will get you the distance from where you are to that point and from that point to the centre of the green. It sounds simple but it's worth its weight in gold when you need to know how far to hit it. For instance, to a layup point or for a recovery shot back into the fairway.
It takes the guesswork out of recovery and layup shots. I've actually found it most useful for those shorter chipouts/pitchouts where you want to be sure to get it all the way to the fairway but not bash it over the other side and right back into more trouble. I use it for that more than for layup yardages. What does that say about my game??
It's also really nice, once you are in sight of the green, to be able to tap the real pin position on the green rather than having to do a mental calculation based on the pin's relation to the front/middle/back measurement.
I am already completely addicted to those last two features that are based on tapping the screen anywhere on the hole or the green to get those yardages. Sufficiently addicted that you would have to pry the G6 from my cold dead hands.
The viewability of the screen must be mentioned. It's a really great screen for bright sunlight. I'm now sure how they do it but it's sort of reflective so even on the brightest days it's easy to view the screen. On sunny days I turn the backlight completely off. As you might expect, that does great things for the battery life, too. The only day I had to turn the backlight on for a few holes it was a really dark dreary overcast day. Normally I won't golf on such a day but we had started the round in better conditions.
The above features of the G6 are good enough that I'm able, most times, to overlook just how truly awful some of the other features are.
Scoring is so-so. It's easy enough to enter your score. Once you figure out how to get there, you can get a hohum summary of your score any time during the round. I don't fault the lack of a more comprehensive scorecard-like display because it would be just awful on that small screen.
But I expected a lot more than you get when it's connected to a PC. Rather than having a proper PC program that you can upload the scores into for analysis and display, it has a hokey HTML script in one of the folders in the G6's internal memory that you run with your browser. All it does is display a list of the rounds and then displays the round you select from the list.
That's it!!!
If you want to get any aggregate information from your scores, like handicap, average scores on par 3s, 4s,5s, percentage birdies, pars, bogies and so on, you are on your own.
Stats are even worse.
The only thing you can track is the number of putts and whether you hit or missed the fairway.
Those who are about to say it also lets you track Greens In Regulation, hold onto your shirts. It doesn't. Specifically, you cannot tell it you hit the green in regulation. It just guesses.
You enter the number of strokes you took on the hole. You enter the number of putts you took on the hole. The G6 subtracts the two and decides whether it thinks you hit the green in regulation. Mostly it works. But it can also be wrong.
Example: the 9th hole at one of the courses I play is a par 3 with a green that slopes steeply from back to front. On Wednesday I hit the green but hit it to the back of the green when there was a front pin. I putted off the front of the green, chipped it close and tapped in for 4. The G6 does not credit me for a GIR. It's wrong.
It doesn't track any other useful stats like bunkers, up-and-downs, sand saves, etc. And there's no way to display any of the stats even if it tracked them.
I know I sound kind of hard on Garmin regarding the scores and stats but this is an expensive device. I should be able to expect better ... a LOT better. Especially when you consider that Android apps you can buy for $2.99 do a lot better than a device that costs a hundred times as much.
As I said at the start, it's wonderful for helping manage your game on the course. The screen is excellent in bright sunlight. And the battery life is great (I haven't tried it but I'm sure I could get three rounds out of it). For those things it's a keeper.
But if Intelligolf ever becomes available for Android I'll be going right back to it for scoring and stats and using the G6 strictly as a range-finder.
I hope that's helpful for anyone considering a Garmin Approach G6.
...ken...