Free-to-play titles don't require a PSN sub to play online, but pretty much every retail title with online play does.
Given the amount of fighting games I play online the subscription is totally worth it for me... although PS+ is the only online service I subscribe to - I gave up my Xboxlive Gold at the start of this gen when it became obvious to me that I would likely never get an Xbone.
The free games are a nice bonus, but they're not the reason to have PS+ - especially since they dropped the PS3 and Vita titles (which often had a PS4 crossplay, so would be an extra PS4 title or 2 each month) from the offer.
It's rare there's anything I'm actually interested in playing from the titles provided (or it's something I already own), but I'd been meaning to pick up Wipeout for a long while now - the original Wipeout being the reason I bought an original Playstation back when it first came out.