It isn't as serious as others (or probably doesn't feel so because of the faces of the characters) and is by far the most polished FF game right there. However, I think that in both writing, story, characters and game mechanics it fall short in comparison to 6 and 7. Which isn't a shame cause (almost) all games fall short in comparison with those two games. It is a great game to start playing FF, though I am not sure that then people will go to play 4 and 6 which while are great games (actually 4 is rated higher than 9 - something that I don't agree with, and 6 is rated higher than everything else bar possibly Chrono Trigger) have bad graphics (compared to PS games which is normal because of platform). I was planning to skip the SNES games, but Redlambs suggested me to play 4 and 6, which in turn was one of the greatest gaming decisions I have ever made.
So, for that, maybe it would have been better to start with 4 and then play all of them till (and inclduding 10). Anyway, regardless of which game he starts playing, it would be a big shame to not play 4 and 6.
My favorites are 7 >= 6 > 9 >= Chrono Trigger > 8 >= 4