I felt the same way when I first played Castlevania: Symphony of the Night. My first game in the series was Harmony of Dissonance, and it blew my balls off, so then I played the other 2 GBA 'vanias, both PS2 games, and the first 2 DS titles. So that's 7 games I played with roughly the same Metroidvania design as it's predecessor, so by the time I played the game that started it all, I wasn't impressed in the least.
I didn't play the games in the franchise in the order they were released, so I didn't see the progression and evolution of it, nor the significance that Symphony of the Night had. I still KIND OF appreciate it, but when I see how its successors improved upon its formula over time, and how much fun the series already was before it came out, it doesn't even rank in my top 5 favorite Castlevanias, let alone games of all time. :/