It's decent, but does not meet the expectations made by the high review score on this site.
It was good and didn't ruin it's predecessor in any way, but it just feels like an expansion and is pretty much dependent on the first for most of its story elements.
The battle system felt slower than Chrono Trigger, because you transported to a battle environment a la Super Mario RPG when you came into contact with an enemy in the field. The fast forward item on New Game+ is a boon since you can now speed through most battles with ease and not waste seeing the same animation over and over. This option should have been there from the start. It didn't help that the battle music was sort of an ear-sore. It definitely could've been better considering it was Yasunori Mitsuda in charge of the music. There are a few favorites though like Voyage - Home World and Star-stealing Girl.
The characters, as tends to be with a roster as large as 44, is very forgettable, basically just swapping avatars and different moves with very little background for each. None of the tight-knit bonding and development between a small group of people here, which is regrettable.
I hate to say it but the villains were kind of lame as well. The final battle was a letdown. It works in terms of story limitations, but is about as epic as a random encounter.
I found myself having the urge to play Chrono Trigger after playing this, and CT just felt more epic and entertaining, even after this time. As has been said, don't expect a Chrono Trigger 2, as I understand it was the developers' intention to offer a new playing experience as opposed to rehashing the predecessor's features.
I'm sure there are many things I missed/forgot, but those are my musings as I write this, and I stand by them. I hope you enjoy the game though, having played CT or not.