I've never played any of them and there is a few reasons for that I guess. One is a perceived similarity to Jak & Daxter, a series I had long ago invested in, enjoyed, and still yet to complete. To me, this sort of left Ratchet looking like an also-ran. Secondly, the sheer number of entries is daunting. I like 3D platformers, but that's a lot of entries for a game that debuted during the PS2 era. Lastly, I've always felt turned away from the games because I found the subtitles hideously juvenile, and thought if the in-game humor was anything similar, I might not be able to stomach it and actually enjoy the game.
But I know there are plenty of Ratchet fans out there. How are the games actually? Good? Worth investing into all 20 sequels? Any that are particularly better than the others? I ask because I finally popped on a cheap copy of "Going Commando" the other day.