Gate of Thunder - An amazing horizontal shmup with perfect gameplay, great graphics, and huge bosses. One of the greatest shmups of all time, imo.
Honorable Mentions must be given to Spriggan (Compile at it's finest), Lords of Thunder (Same dev team responsible for Gate of Thunder), and Star Parodia (vertical cute-em-up, based on the Star Soldier series). Sapphire is also quite the quality game and it has 2-player co-op, but you'll find it's a bit on pricey side trying to get ahold of this one. I'm also a bit partial to Psychic Storm, as it's like a 2-player co-op CyberCore on steroids. This is not to say these are the ONLY great games on the PCE-CD, but these would have to be my picks as must-haves.
Also, as biased as I am (I'm part of the dev team), Meteor Blaster DX is a worthy game, especially for those who enjoy remakes of classic arcade games. It's basically Asteroids that's been juiced up with power-ups, bosses, and vastly improved graphics (somewhat like Blasteroids). I would say it holds it's own against other classic shmup remakes on the PCE like Galaga '88, and Space Invaders Original... but as I said, I am biased.
