It's very good. A tad easy on the default, though.
I'm a sucker for Compile.
I don't know if I listed them in any particular order. I go back and forth, depending on my mood. Recca is the most intense in places, but Zanac is an endurance meatgrinder that really separates the men from the boys.
I'd also toss in Konami's shooters like Gradius II, Life Force and Crisis Force. Konami always struggled with slow-down, though. Especially in the original Gradius. Level five is almost unplayable.
Uchuu Keibitai by HAL is another great looking shooter.
Some flawed shooters I still like are Exed Exes, B-Wings, and Argus. I also like Super Xevious for its puzzle elements (you have to solve a certain condition to progress) and Super Star Force, even though I have no idea what I'm doing in that game.