blades your disappointed with

For me it's Voshkod and Rapira

Rapira Swedish Steel for me, but I love the Rapira Platinum Lux blades, so much so that I bought 100!

Both Astra blades continually disappoint me. I try them every other year and still no good for me.

Personna stainless steel comfort coated. Also Merkur & Voshod blades.

Derby Extra (Green) are bad in just about everything I try, albeit for one exception. I don't know why it is, but they work really well in open comb razors!

Derby Extra (Green) are bad in just about everything I try, albeit for one exception. I don't know why it is, but they work really well in open comb razors!

I didn't like Derby green Extra blades either but it did work well in the Muhle r41 for me.   

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I'd like to mention that Merkur blades weren't very good for my shaves.

A mystery blade for sure. I never felt too comfortable with the M41 when I first used it but might be a different story now. Merkur blades I can't give too good an impression on as I only used the few I got with Merkur razors, but never found it too good. Considering the price too I'm not keen on giving them another chance.

I have a tough beard, so I need very sharp blades. I have sensitive skin, so I need smooth blades.

Blades that do not work for me because they are not sharp enough:

Derby Extra, Shark Super Chrome, Durablade 7 AM, Merkur, Van der Hagen, Gillette Rubie Plus, Astra Super Platinum (I can use this one if I had to do so, but prefer not to use them)
Personna Comfort Coated (lab blue) on the first shave; as coating wears off, they work fine

Blades that do not work for me because they are not smooth enough:

Feather Hi Stainless- work for two shaves and then become too rough
Astra SP blades and Gillette Rubie Plus are not particularly smooth along with their lack of sharpness

I don’t know about disappointment in a blade but I do have several in the “not really a razor blade” category and Merkur leads that pack.  The only blade I can think of in terms of disappointment is Bic.  I do best with the sharpest blades and it’s reported that Bic is one of the sharpest but I’ve tried them two different times and found them nearer a Merkur than a feather and it puzzles me.  Perhaps I need to try them yet again.

This is  an interesting thread. Disappointment suggests an unmet expectation so to find a blade disappointing I have to first have an expectation of better performance than it turned out to have. By that definition I really don’t find any blades disappointing but there are plenty that I find ineffective in the razors I have tried them in. That said, I can certainly see where a person might be disappointed if say, I highly recommended my favourite Feather blades to them saying how fantastic I thought they were and they went out and bought a 100 lot only to find that they didn’t like them. That’s disappointing, incomprehensible in my opinion but certainly disappointing from their perspective.

Voshkod for sure