D&D 4E A couple of things that suck about the 4e SRD/OGL

[Ranger REG]

Well...if that's the case, and you can use rules, why even bother with the OGL at all?! In fact, you'd probably be safer if you didn't use any OGL for that--I suspect if you were using a OGL that Wizards says is specifically not applicable to 4e, you'll have less protection than you would if you didn't use a license at all and claimed "game rules are not copyrightable".

You could but the copy-n-paste publishing that the SRD -- and the MSRD -- provides cuts down game design time.

The only thing you're left with is writing out IYOW, the character creation and advancement rules, as well as fluff to appeal your product to interested buyers.