I think the difficulty of Blazing Lazers in its later levels is tuned to be challenging, but not overly frustrating. I'm not that good at shooters, but this game gives me the feeling that I should be able to beat it someday.
R-Type however is just sadistic. It lures you with it's quite manageable first half and then it throws you on the ground, breaks your limbs, cuts off your dick and shits in your face while laughing.
The same happens in R-Type II and III, but this time even sooner in the 2nd level.