It's pretty fun, I think. The slowdown hurts a bit at first, but it's easy to get used to it after some time and you may actually have an advantage when you reach the later stages - you'll definitely be thankful! Also, you don't get to see very many arena-based shmups at all (especially back when the game was released), so this one's got a bit of originality going for it along with a sense of urgency as you're ALWAYS racing the clock! It's a pretty solid game with only a few rough edges, so I'd give it a 7/10.
I haven't played it in years but now that I'm reminded that I have a disc copy somewhere in my closet, I'll dig it out tomorrow and start playing it again.