Stability: So far it has not crashed.
Learning curve: Steep due mostly to the problems with navigation and the lack of a professional tutorial.
Ease of use: Workflow SUCKS! Very geeky due to a poor layout. Hard to find which track have effects on them with a simple click in the track channel like most other DAWS hence the geekiness.
Effects: Some are good, some are bad and some suck.
Value: They have a free version but remember time is money.
Overall: If you have the time to learn this Rube Goldberg style DAW you may get some good results from it. If you like counter intuitive geekware and mediocre effects and VSTi you will love this DAW. If you are a musician you will find it retarded and frustrating. If you take the time learn which is like have a wisdom tooth removed through your asshole, Studio One may grow on you but don't count on it.
I may have been a bit harsh I may have been a bit harsh regarding studio one. Compared to other DAWs you don't read about all the crashes and bugs. The plug-ins are is good if not better than what you'll find in other digital audio workstations and when it comes to bang for the buck studio one is a clear winner. It is stable. You rarely read about it crashing and it did not crash on my computer here in with a lot of other applications running. The native plug-ins don't seem to cause the freezes and crashes so common with other DAWs.
The biggest drawback with studio one is a lack of a tutorial and well written manual. With that, it's hard for me to actually describe quality of the workflow. I don't like the GUI very much but perhaps if I can learn it better the workflow may prove to be good. It still has a very high geek factor.