To be honest i don't remember when and where i heard about im@s the first time. My best guess is that i read something about it on kotaku when Live for You was about to be released which would put it around end 2007/beginning of 2008. I looked up some videos on Youtube and was really impressed by the smoothness of the animations. I was interested in trying the game, but i didn't have a japanese XBox back then. Since the games were also available on the XBox live market place i tried a lot to trick the region lock. I don't remember how many hours i spent on buying money on the japanese market place, hooking up my laptop with a japanese VPN and routing the XBox internet connection through my laptop to fake a japanese IP. I think i managed to actually buy the game this way, but it couldn't install it due to the hardware region lock (i got past the IP region look iirc). So i reluctantly put that project to rest, but my interest for im@s was there to stay.
When i found out about Dearly Stars being released and being a DS game it didn't have region lock (i didn't have a PSP back then so i didn't buy SP which was released half a year earlier) i went on play asia and placed a pre-order for it on 31th of August 2009, about 2 weeks before the games release. I think i started with Eri as idol, but quickly switched to Ai. But unfortunately, unlike most other im@s games, Dearly Stars doesn't offer you much if you don't speak Japanese, which i hardly didn't back then. So i put it away after a bunch of hours, but i definitely was hooked on im@s now.
Another 2 years later there was an announcement of im@s 2 on the PS3, which was the final reason that made me buy a PS3, and of course i ordered the limited edition of the game as soon as possible (the one that came with G4U vol 1 and the first anime BluRay, unfortunately CD japan screwed up and forgot to add the film strip to my order

)
Towards the end of my 10th playthrough (Yukiho normal end, a deliberate Yayoi bad end, hyper mode and 7 good ends) and over 100 hours i wanted to actually understand what was going on in the story. More than just the very very basics i understood with my Japanese knowledge back then. This was the final reason why i took up formal Japanese lessons (in class/with private teacher) again, after a break of 13 years and several failed attempts of self studying. I wanted to have something to force me to keep at it, since i always kept saying "i'll do it tomorrow" when i tried to self study, and having a weekly class was something i couldn't just push off to another day. So at that point i definitely was a serious im@s fan.
I didn't finish that 10th playthrough (Chihaya btw) until about 1.5 years later, when i thought my Japanese was ready now. I then also finished the remaining routes, and then went for the Yukiho good end i deliberately kept until the very end.
This is one reason why im@s is really special to me, it was the reason why i finally brought my Japanese to a level where i can easily talk to people, play games, read books and so on.
From there on, i bought a lot of stuff around im@s, including the full set of limited edition BluRays (including all G4U volumes), figurines, games and a bunch of CDs. And i always dreamed of going to one of the concerts.
The mobile games never really interested me, since they lack gameplay. I tried ML for a bit, but since it was simply screen tapping i gave it up quickly.
When 10th was announced, i decided to not continue simply dreaming of going to an im@s live, but to actually try and go, it was the 10 years anniversary after all. Through animagic4u i was invited to HPT (Houkago P Time), and there i learned a whole other level of im@s fandom (calls, pen lights, UOs, producer cards and more), and i was inevitably drawn into it. Going to 10th really has been on of the best experiences in my life by being able to go all out about im@s and sharing all this with other im@s fans. So far i never met another fan and i don't know if there are any others in Switzerland at all. So meeting up with the people from HPT and spend time with them in Akiba, game centers, for meals, in line for buppan and at the concert itself was a real blast, especially animagic4u and her boyfriend, Leo, Menchi, Mizuki, Mahouko and Azu were fun to hang out with.
Apart from the people there was the im@s theme cafe which itself is kind of a mini live and the im@s songs only karaoke which were also a lot of fun.
And there was buppan, the sales of 10th anniversary concert goods on Friday before the concert. I got up at 04:15, got on the train on 05:02, arrived at Seibu Dome around 6, and then lined up and waited. There were already about 2000 people before me in the line and sales started at 10. But the waiting wasn't so bad, since there were a lot of people around to talk with and who also had to kill time. At 12:15 it was finally my time to buy stuff, and i spent over 70'000 Yen. The only regret i have is that i forgot to buy a 10th commemorative towel. But first an foremost, i got my hands on the 765pro 10th penlights:

And then i lined up at the other line (alone this time) and waited for another 2 hours to buy the 3 special CDs.
And of course there was the concert itself... And it blasted me away. The depiction in the game or the anime with the people boasting penlights and UOs (ultra oranges, glow sticks you "break" and then they glow brightly for about 2 minutes and then start to fade off quickly) and doing calls (those "hey, hey, hey" and so on shouts) are not an exaggeration, in contrary, they are much more prominent at an actual concert. You are not simply watching an im@s concert, you are part of it, and it is amazing.
And then there were also the really emotional moments that moved me to tears and still do when i think about them. Starting with Haruka's seiyuu shouting "Producer, domu desu yo! Domu!", to Azumin (Yukiho's seiyuu) shouting "Yaaaaaay!!!!" before starting to sing Alright* (just like in the anime episode), Iori's seiyuu's voice caving in and starting to cry during matane and the whole dome shouting "gambare!", immediately followed by Azumin (Yukiho) performing first step (which is a really special song to begin with since it appears in Yukiho's story in im@s 2, being written by Yukiho in game, and by Azumin herself for Yukiho in reality) and almost starting to cry as well, the announcment of the original cast still being in the PS4 game, up to the talk between the seiyuus of Haruka, Chihaya, Iori, Azusa, Ami/Mami and Makoto about how they started off 10 years ago and how they never expected to stand in a dome in front of 40'000 people when they auditioned for the arcade game.
Going to 10th made me an even more hardcore im@s fan, and if i can i'll go to 11th as well, i don't care about the cost (living in Switzerland, being a programmer and single helps a lot with the cost point though).
So much about my history with im@s (i wrote way too much and it took me 2 hours...).
Up to this point, im@s is first and foremost about the characters for me, and everything else is connected to them (the games, the music, the anime, the concerts). This is why i need something to get me into the characters, and why i'm still not into CG and ML. On the other hand 876pro had something to flesh the characters out and make them dear to me (first and foremost Ai). Because of this and because i still couldn't get into the CG and ML characters, i'm really happy that the PS4 game will use the original cast.
About CG and ML: I need something to get me invested into the characters, something that fleshes out these characters and puts some meat on their bones.
I was hoping for the CG anime would do that for me, but so far it doesn't, since it failed to explore and develop most of the characters, and the ones it did don't interest me. My impressions are "average anime main girl" Uzuki , "wannabe Chihaya" Rin, "faceless Sidekick" Mio and "pointless chuuni" Ranko. Sorry to the fans if i got any of the names wrong, but that just shows how bad of a job the anime is doing in selling those girls to me.
So my current hope rests on Starlight Stage, since i really would like to get into the spin offs.
On a side not about the characters: Originally i only had the visuals as a reference and i was most interested in Iori, although the bunny always irritated me, so it was a tie between Yukiho and Iori. When i found out about Iori's character (which was quite early) she immediately went to rock bottom in my popularity list and still is there.
And i really have to copy animagic4u here:
アイマス最高!