So I've been playing the piano for about 13 years now and I've noticed the action of my piano getting worse and worse. There are actually several problems:
On some keys the amount of force needed to move the keys (& hammers) is relatively high at the beginning and then after slight movement rapidly reduces, which in turn reduces the dynamic range of that tone since it either comes out too loud or not at all.
As said, problem 1 only exists on some keys which completely messes up the general key weights. While the keys should usually just slightly increase in terms of weight towards the lower registers, on my piano you can find lots of adjacent keys where one of the two is ~40% harder to press than the other. Playing trills on two keys like this is just horrible, but even simple runs can throw you off completely when coming across* keys like these.
* It's about every third key I'm talking about so coming across them doesn't take long.
To counteract these problems I tend to hold down the soft pedal since that kind of evens out the problematic key weights, gives me back lots of dynamic range and brings the feel of my upright much closer to the Yamaha Grand Piano I had piano lessons on until recently. But this can't be the solution in the long run.
I should say that for the time I've had this piano (~10-11 years) it has never been adjusted and I believe this might be the reason. So would a simple adjustment do the trick or is there more to it? It would also be nice if anyone could tell me what exactly in the key mechanism is causing these problems.