Buy it for the golf, not the 3D
The artistic design is absolutely stunning. The courses are so beautiful, particularly the Kenyan ones with a breathtaking African sun and the Greenland courses with amazing Nordic lights. The 3D is pretty bad though. To be fair, it does make it easier to see the curves, so I often put it on when putting, but even with the 3D on it is harder to judge the curves on this game then Mario Golf, so I hardly consider that a plus.
Like with Mario Golf, you hit the ball by pressing the A button with good timing to first set the strength, then the accuracy of your shot. However while in Mario Golf you could put a spin on the ball before the shot, in LG 3D you can use the slide pad to put a spin on it while it is in the air. The team at Gameloft has done a good job of balancing this so that you effect the ball enough that it makes a difference, but not so much that it doesn't matter how well you timed the strength and accuracy in the first place.
While you need the skill to make the ball go as far as you want, you must also figure out how the curves, the wind and different surfaces will effect the distance and how far it will bounce after it hits the ground. This is what made MG challenging, and it is done as well or better in Let's Golf 3D. LG depends less on math though. In MG the different clubs had different distances, like say one hit the ball 114yards and one 128y, so if you needed to hit it 120 yards you would have to choose the 128y club, then hit it with not quite maximum strength. In LG you can aim it at 120y, then the game will do the calculations for you. LG also adds special moves, which your character can use once he or she has filled a bar. One I found useful is "Strong Magnetics" which makes it so that the ball will not bounce after it hits the ground.
The main mode in singleplayer is the career mode. For each country there are seven different tournaments and in addition three courses in each country has a gold medal somewhere that you need to find. Those aren't that hard to find if you look for them, but they do require that you put in the effort. The tournaments vary from stroke (normal golf where you need to get the lowest possible shots on a given amount of hills), to shootout (where one golfer is eliminated per hole), close to the pin (where you get one shot on each of three 3 par courses and the one with the lowest combined distance from the pin wins) and matchplay (where it is you against a computer and it is best out of seven courses, where you win, lose or tie on each of them). Except close to the pin, there is also a timed version of each of those, where you have less than twenty seconds on each shot.
The career mode have a nice amount of variety, and while it is generally easy (sometimes very easy) some of the tournaments are pretty challenging. Apart from the career mode, there is the challenges with four different types and five levels for each of them. There is one were you need to get from the bunker to the hole on a limited amount of shots, one where you have limited time to get birdie, one where you collect four letters (GOLF) and a putting challenge. It doesn't last very long, but it is neat. There is also a "free hole" mode in which you set up the tournament yourself and then play and last, but not least there is two player (locally, with only one 3DS required)
The game has an achievement system which is a good idea, but somewhat flawed. You get different amount of points for different achievements and the goal is to get a hundred percent complete rate. There are some achievements for just playing something for the first time, you also get some for completing career and challenge mode, which are all things you would do anyway. There are some achievement that does add to the experience. For instance scoring a "double eagle" (also known as albatross) which is to complete a 5 par course in two shots or to get a hole in one, which took some work. A challenge for competing an 18 hole tournament on hard in only 60 strokes (12 under par) is a nice challenge and I can even agree on the one for hitting the water 25 times during a tournament.
But then there is the challenge for winning a 100 matches in two player. Consider that by "match" they mean a tournament, which is at least a best out of nine, so it can be over after five holes if the same person wins all the time. I tried to complete one tournament as fast as possible and had a good round with three eagles and a double eagle, and I still used 9 minutes and 40 second because of long loading screens and having to play both characters. If I were to complete 100 of those, and all of them as fast, it would take 16 hours. That is just ridiculous. Achievements is good for adding incentive to singleplayer, and thus you should be able to complete all of it in singleplayer. When I have someone to play multiplayer with I don't need any motivation and I'm mad that after spending 18 hours on beating career and challenge hundred percent, plus getting other achievements I still have 16 hours left if I want to get a hundred percent completion.
Bottom line is I really love Let's Golf 3D. It has a couple of bugs where you can't aim where you want, it occasionally lags during the computer's turn at match play and the loading screens are pretty long, but the gameplay is solid, the graphics are amazing and the music is also pretty sweet. Also, 18 hours of singleplayer, plus possibility to play multiplayer is great for a game that only costs 6 euros or 7 USD.
It is hard not to compare this game to Mario Golf, so I'm going to use this last paragraph to compare LG 3D and MG for the N64 (haven't played it on Game cube). Well, LG has way better graphics and I also think the gameplay is better, despite it being harder to judge the curves. Mario Golf has better music and it is more memorable to unlock characters. It also has more variation with modes like ring golf and time golf. Mario Golf has up to four players in multiplayer and has stuff like the slot mode. I also really enjoyed the mini-golf in MG. MG had a flaw in that you could cheat the game by saving when you were about to do poorly on a hole and restart at the beginning of the hole. The only way to take a break in LG is to close the 3DS. LG also has a better way to save videos. While MG saved your five most recent birdies, eagles, hole in ones and albatroses, in LG you can choose which once to save and store up to 16 replays. MG has slightly better course design and I also like that in MG you could sometimes start next to the water when you hit it. LG has RPG elements that add a little bit to the experience, but not a lot. All in all I'd have to say I like Mario Golf better, but if Let's Golf 3D had all the same modes MG does, it would be the victor.