Someone a month or 2 ago posted the snowball effect relating to judging the PS4 games library - It was something like - if you take away the first party titles I don't want and crossgen games as well as indie titles (because indie games aren't real games) then the PS4 has no games !
I'd say buying a PS4 from last years launch all the way until even next fall , you are buying a new console to have a new console. There are plenty of games, tons of excellent indie titles to play and cross gen or no- the best looking console versions of any multiplatform title are on the PS4. If you haven't bought into the promise of future releases being of higher quality than sony's output so far (infamous SS notwithstanding) or you just flat out honestly hate indie games (for some reason) and you are content playing games on last gen hardware OR have a decent PC then yeah, it might be a better idea to keep waiting. If you do fit that criteria and bought a console anyways though, why ?
I know I picked one up simply because I wanted a new thing, infamous had just released and looked pretty good and there were a handful of downloadable games I figured I may as well play on the new hardware as well as knowing full well that there would be a few exclusive titles in the future I'd want to play. Even if it was 2 years out.
Would I recommend the purchase of a PS4 though ? honestly I'd say the only next gen system worth owning right now is a wii U. It has TONS of exclusive games , mostly made by nintendo and the majority of them are great. As well, you can play standard wii games on the hardware as well as have access to hundreds of virtual console titles.
I feel buying a PS4 or an xbox one for that matter is best left for next fall, by then the first true heavy hitters will be out on both systems and there'll be a cheap back catalog of everything else. As well, I feel after 2015 the wii U doesn't have much of a future so it's better to get into that machine now rather then waiting until it dies.