Good, but not as good as you once expected from HP. Speed demons beware!

If (like me) you had the privilege of owning/using HP's legendary 41C/CV programmable calculators, you've probably been looking for a worthy successor ever since. Well the reality (in my opinion) is that no HP calculator released since the 41C has ever equalled it in terms of speed, capability, reliability or general user-friendliness. The 42S was pretty good, but some of the ones that followed it were downright terrible. This one's not bad, both in terms of quality and capability.
I owned an HP48G for a while, and although it had awesome capabilities, it was just too slow in everyday use - it seemed to take an age to respond to key inputs which made entry of fast, complex calculations (like in an exam) almost impossible. I flogged it and bought the 42S and then the 32S, both of which lasted only a few years each before breaking.
Like many engineers, I prefer using RPN (Reverse Polish Notation) and the number of HP calculators that still offering it is dwindling - unfortunately the (unenlightened) masses mostly want algebraic entry. The 35S seems to be the only one on offer right now.
Nowadays I mostly use my calculator for the odd desktop calculation - anything more complicated and I open up Excel, MathCAD or something similar. In that kind of use, the 35S is fine - it has all the mathematical functions you expect and need, especially if you're studying Science or Engineering. And if you do need to go further, the 35S offers fairly advanced programming capability as well, although I haven't exercised it its fullest extent.
The main gripe I have with the 35S is the quality of the keys - they're good, but if you were used to the legendary tactile-feedback keys of the early HP's, you'll be slightly disappointed. When entering a string of digits fast, it's not uncommon to have the 35S miss one or two, either due to a faulty keypress or to the CPU missing the entry. It's not a huge problem, but it does mean that you have to check the display before proceeding - something that was never necessary on a 41C.
Apart from that gripe, this is a good-quality, very capable scientific calculator that responds reasonably fast. If you want an HP RPN scientific calculator, this is it - buy with confidence.