Xenon2 for sure. It got reviews pretty high. defined as the best vertical shootemup ever. Even rereleased with that slogan. but I do not know anyone who truely liked it.
Also I would add JimPower. it got great reviews at least here in spain, but the game has horrible sprites, ugly (with exceptions) backgrounds and a very doubtable gameplay and level design.
BloodMoney also got great reviews, but I guess Im the only man who liked it. (also I must to confess that I arrived to endlevel boss to Xenon2 without cheat)
IronLord and DefenderOfTheCrown I guess they are nearly as playables as SpaceAce or DragonsīLair games.