Solid!! Nice work! I've seen plenty of times where stairs (or single steps) were an after thought, thrown together with scraps, odds and ends, etc. They are a high traffic, high impact areas and need to be as beefy as possible.
Nice work. My two cents. Instead of stringers it would have been less labor intensive to build several long rectangular boxes of the different riser heights and securing them together. Good point about being able to reuse old screws of torx head type. Forget about Phillips screws, they cost less but strip out more often.
