Huh, I didnt even see this topic before. I'm a fan of the series myself. First horror games in.... freaking forever... to have ever even gotten me nervous or anything like that. The only other one that ever managed that was Eternal Darkness on the GameCube (absolutely fantastic game, that one, I loved it).
I really like the gameplay concepts that Scott came up with; the whole idea of you not having real weapons OR much in the way of real defenses, yet you still had to somehow deal with these unstoppable nightmare bots. So you use the security cameras to track, and thus respond, to their movements. The idea, to me, is brilliant.
Though, it took alot of refinement to get to where the developer seemed to want to to be. The first game could be totally beaten by simple repetition of the exact same 3-4 actions... you didnt need to do anything with the camera aside from keep Foxy somewhat under control (oddly, though, Freddy himself seems to glitch out throughout this process, as you're SUPPOSED to keep an eye on him to slow him down and stuff, but it's almost like his AI vacates the area as he'll never, ever attack if you keep up that sequence despite ignoring him). The second game tried some new things, but it still ended up suffering from the same problem. The third, however, does not. It seems to be the very sort of gameplay that the developer was after in the first place, since you have to actually USE the cameras to track and respond to your foe. And it's just freaking brilliant.
Now as for what I've played, I have all three games. I've played well into the first one.... generally I'm trying to go through it all the way without using the left light, right light, check foxy, repeat exploit; I keep getting clobbered by stupid Chica though. I dont know why it's always Chica.
Second one I've only played a bit of so far; I got too distracted by other games. Which happens to me sometimes.
Number three I havent tried yet, but I already bought.
I have seen all of the currently known story elements though. Getting the other ending in number 3 is.... such an incredibly convoluted process. I dont know how the heck anyone managed to figure that out! I wont drop any spoilers here, but.... it's pretty messed up. And what impresses me is that all of the secret minigames, despite their ancient style of graphics, manage to be creepy and unsettling as heck ANYWAY. The minigames in the second game struck me as being that way too. It's possible that there's actually a third ending though as well. Nobody seems to be quite sure about it.
Even with all of that though, there's still tons of unanswered questions that makes me wonder what the developer might do with the series later on. I cant see him making a direct sequel, as it's extremely clear at the end of the third game that the main string of events ends after that (well, probably). But I wouldnt be surprised if he ends up doing another game that doesnt play anything like these... and may be a different genre of gameplay entirely (yet still retain the horror theme), that goes into more of the backstory that the player doesnt directly experience or witness at any point in the 3 main games. Like the original restaurant: You never, ever see it, but there's a TON of hints that something seriously messed up happened there (particularly the fact that the bots in number 2 are possessed at all, is the biggest hint, but there are others). And tons of other questions too, though I cant really mention any without spoilers.
The whole thing is fascinating. Normally I dont really get into the story elements of most games... but that's because most games dont tell them well, and they often just arent even written very well. This series does it in more of the way that I personally wish other games would do. It's different than the usual long, rambly, flashy cutscenes that basically every other game ever does.