JRPGish thing with mild 'dating sim' aspects, if you didn't know.
I really enjoyed Persona 3 Portable on the PSP, so when I finally picked up a vita, this was high on my list of games to get. Straight off the bat, I wasn't as interested in the theme (murder mystery), and while the first couple of hours are 'slow' (all character introduction/story, no combat), I personally prefer that to the actual dungeons anyway.
When I got a couple of dungeons in, I must have been fairly underlevelled because the boss wrecked me. Eventually they'd do one move which was a complete party wipe, with no warning phase. I tried many times to get past it, to no avail. I was annoyed enough that I put the game on the shelf for months.
Eventually I tried again and managed to get past that point - the next dungeon I encountered I grinded levels for something on the order of 3 hours to get up to a decent level so I didn't have to go through that again. As I understand, this is atypical though, no-one seems to need to grind at all in p4g, so I don't know what I did wrong. Maybe I was avoiding a bunch of combat because I didn't really like it that much, and then avoided it more because I was underlevelled. So - do your combat, kids. Stay in dungeon.
Anyway, I still wasn't particularly invested in the early characters or story. It wasn't until about 40hrs in that characters I really liked showed up, the story became properly interesting, and my abilities in combat became varied enough that I was properly enjoying myself. Subjective, obviously.
From there on out until the end (~85hrs all told), my party was a bit of a wrecking crew in dungeons and the story was good. I feel perhaps more choice should have been given to your 'post gameplay' actions, and I also would have liked to be able to, er... disengage... from relationships, so that I didn't feel like quite such a scumbag when my true waifu finally appeared and I had some unimpressed suitors on Valentine's day. Luckily they are only video game characters and aren't really jilted. Right? Please?
Anyway, overall I liked P3P more for the setting/story and most of the characters (except that annoying fool Junpei). P4G has better music though (that being said, P3P's was outstanding as well), and there were some gameplay improvements during the dungeons. The presentation in general (art, style, music) is simply fantastic, and looks outstanding on the Vita's screen. The only place this isn't quite true are the Anime cut-scenes, which look decidedly low budget in comparison, and also annoyingly don't have subtitles! Blargh!
A year and a half elapsed from initial boot up until I finished it.