I've been a subscriber for about 4½, years, and I'm quite satisfied with it.
The selection of games is huge, with over 900 games available now. I'd say just about anyone can find something to play. I'd estimate that about 550 of the games on the service are PS3 games (which are only available for streaming), while the remainder are PS4 or PS2 games (can be downloaded on PS4, or streamed to either PS4 or PC).
Streaming is extremely convenient, since you can choose your game from the menu, and be playing in a minute or less. This is great when you just want to play, and don't feel like waiting for 40 gigs to download.
The streaming quality has gradually increased throughout the years. The are far less instances of hiccups or artifacting now, compared to when I first joined.
While I feel the service is great for what it is (especially at the price point it's at now), there's still room for improvement. Here are some of my suggestions:
1. Bring game streaming to a wider range of devices. It should be on mobile phones, tablets, Roku, Fire TV, Apple TV, and so on.
2. Increase streaming resolution to 1080p or higher.
3. Allow you to purchase games through PlayStation Store, and stream them through PS Now (similar to how Stadia works now). This probably would be difficult to negotiate licensing rights to the thousands of games that are currently on PS Store, but surely Sony can figure out how to negotiate this for future releases. As far as existing games go, they should extend the invitation to game publishers to negotiate the rights for individual games on a case-by-case basis.
4. Add many more PlayStation 2 games, and also games from PS1, PSP, and PS Vita.
5. Sony used to regularly add 10 or more games to PS Now each month, but since they reduced the price last year, they've also greatly reduced the number of new games. Many months have only had 3 or 4 new games added, most of which are "big" games, but I miss some of the smaller, lesser-known games that would pop up. I'd like to see them bring back more smaller games or indie titles (which looks like something they're starting to do now).
6. They usually dump the whole lump of games at the top of the month, and then (with very rare exceptions) don't bother adding anything else until the next month begins. They could instead stagger the releases, and roll out at least 2 or 3 games each week. This gives users something to look forward on a weekly basis, and keeps PS Now as a frequent topic of conversation.