After playing through Golf Adventure I played a full round (18 holes) on each course with the Standard Golf mode. I played against 3 random AI opponents. This made me realize two things. First, the thing I would have like added is a set of tournaments, like those in Mario Tennis Aces. As far as I can tell there is no way to change the difficulty of the AI and they are pretty bad, averaging +10 per game. As you go through the courses they do get harder so while I started with a score around -10, by the last course I was breaking even. Since the AI do about the same on each course there is some felling of them getting more difficult but the game was never close. The other thing I realized is that you can unlock star clubs. These are leveled up sets of clubs assigned to each character. I played the 72 holes I mentioned above and was able to get about 1000 character points which unlocked the star clubs for Rosalina, the character I have been using. To get the double star clubs you need 3000 character points! This is quite a lot of playing and this is for one character. To unlock all the clubs for all the characters would require a lot of playing. I think it is too slow, much like the unlocks in Mario Kart 8.
I just tried out the Battle Golf mode tonight and it was okay. Probably better with real people. The games are very short and there are only two courses. Next up is Speed Golf with each course. I know GK mentioned not liking XC golf but I kind of liked it. The only problem is it appears to only occur in the Golf Adventure. I can see this being added as an additional mode later though.