No, it really isn't. The language is through-and-through a Romance language, in grammar, phonetics, sound changes and vocabulary. It had some Frankish influence in some areas of vocabulary and perhaps certain phonological tendencies (the biggest being the reduction of unstressed syllables -- typical of Germanic languages, but also shared partly by other Romance languages) and maybe the V2 word order. But it's really hard to find even evidence of heavy influence in any aspect of the language. If you want to point out some things that are core parts of Old French that were derived from Frankish or heavily influence by it, I'd be happy to look at it.
You have to remember that the Frankish invaders were relatively small in number and did not settle much in Gaul. They were a warrior elite, supported by a Gallo-Roman aristocracy, and they were quickly subsumed into the culture and eventually language of the region. It's much different from, say, Britain where the Germanic invaders must have come in great enough numbers to displace the language and culture of the sub-Roman Britons. Notably, Old English, a very much Germanic language, came out of that period, not some sort of Celtic or hybrid. If your claim is true, Old French would look a lot more like Frankish or Old High German or Old English, but it absolutely does not. Having studied those languages, I can confidently say that Old French looks a lot like watered down Latin.