Oh c'mon, of course it was worth it! It is an essential part of the Kingdom Hearts trilogy! You NEED it's story to complete the trilogy's plot. Without it, you won't get what's the deal with Sora at the start of KH2, who Namine is, and you won't meet the COM branch of the Org. (OK, Axel does appear in KH2 but he's expelled from the Org. toward the start and is his own character throughout the game. In COM he's actually an Org. member and Sora actually fights him, which never happens in KH2 unless you count Roxas as Sora...)
That's how the trilogy works...kinda like a sandwich with two PS2 games and a GBA game in-between. The way I see it, although it's the weakest of the trilogy, it's still a 9.0 (with KH1 at a 9.5, and KH2 at a 10.0!).