What introduced me into bishoujo games…?
I’m going to go one big step farther and write how I began to purchase B-games…
My first title…? I guess maybe pirating X-Change 1, like 10 years ago or whenever… Back then it was just for… the visuals and … SFX really lol. That game and many similar games (and some H anime) I simply downloaded whether it was english or not, just cause I was a young teen interested in that kind of thing.
I never knew anything about the localizing company or much else about the game.
Around this time I was playing games like Baldur’s Gate 2 and Morrowind… And these games which I absolutely LOVED, had mods that were sometimes romances. When I realllly enjoyed them, I think it began to directly introduce me to that kind of game. Lots of story, choices that affect the outcome… good or bad.
Also, I started buying some anime in the early 2000s; and eventually I ran into Rightstuf.com when I began to order online instead of retail stores.
I also had gotten interested in mods or translations for my favorite games, which lead me to follow the fan communities, and actively keep tabs on the latest projects people were working on.
In the mid 2000s, I was browsing Rightstuf, when I somehow noticed “Phantom of the Inferno DVD Game”. I was intrigued. Only if a title really catches my eye do I buy it without researching it. It was a good price, and I thought the DVD game for your DVD player, was a really nice idea. (Not everyone has a game console, but most people have DVD players… Also, the cover art caught me.) So, I added it to my order and held onto the game after getting it, before playing it much later…
Around that time I ran into my first VN english fan-translations from Insani… Specifically Planetarian. I was moved by their work (and demo?); with their call to purchase the game legally (for something like 7-10$?); and proceeded to love the kinetic novel Planetarian… cry
Then sometime after, I played Nitro+'s Phantom DVD, and fell in LOVE with Ein. [NEVER had I been so moved by such a terrible set of events… My player froze at the end of Chapter 1, and I thought I had just gotten the BEST bad ending ever. Needless to say I was completely hooked on VNs then.] But, my interest was in non-H VNs, I still wasn’t paying for 18+ games. Bringing that content into the household was probably forbidden anyways… (btw I think I had read the “please support the official localization community message” JAST includes at some point.)
Fast-forward as I learnt about Hirameki and more VN fan projects. I bought most of Hirameki’s titles, learnt about Peach Princess, JAST, G-collections and began to watch their titles …
It wasn’t until the annoucement of “Yume Miru Kusuri” and “X-Change Alternative”, did I suddenly have a change of heart. I was blown away by the quality of game; art, music and reviews of Yume Miru Kusuri and X-Change Alternative. Already had I played games like Ever17, but at this point I finally ordered (pre-ordered?) Yume Miru Kusuri and Alternative.
Upon recieving and playing said games I was not disappointed. And ever since I’ve purchased 18+ games as well as all-ages.
I now have a fair collection …
PIC
And am a great fan of quality bishoujo games 
EDIT: Oh top 3?
No long winded answer for this 
Utawarerumono
Phantom of Inferno
Tsukihime
(runner up : Yume Miru Kusuri)