You're asking if it's a good idea to get a letter of recommendation from a professor that nearly failed you?

No snark intended, but if you nearly failed one of the few classes you were really engaged in, why do you want to go to grad school?

As for the request itself, it's always a good idea to couch such requests explicitly, in terms such as: "Would you be comfortable if I were to list you as a reference for__? Do you think you would be able to give me a good recommendation?" This applies to job references as well. And be prepared to accept "no" with grace and understanding.

If the professor isn't an asshole, he or she wouldn't have agreed to write you a recommendation if he or she didn't think he or she could write you a good letter in good conscience.

However, the professor might be an asshole, or just unwilling to tell you "no".

He hasn't actually agreed yet; I'm supposed to see him tomorrow about details and honestly I'm expecting a "no". But would it be better to get a recommendation from a professor whose class I did well in but barely talked to?

I want to do grad school because if I get a job immediately after graduating it will likely be in the low end of the industry and I'll hate it.

Ah - I think I get the picture, now. Yes, my favorite classes and profs were not necessarily the ones I scored highest with, either.

Well, it seems to me that this is really the type of question that only the professor can answer, so be sure to be direct. I have given references for many people in the job arena, and insist on being honest when I do so. I have therefore also told more than one person that they probably shouldn't use me as a reference.

In general, I think it would be better to receive a more personal recommendation from a well-regarded prof who had challenged you than a generic recommendation from a prof who barely remembers you - assuming such a prof were really willing to recommend you.

But that's just a guess. Departmental politics might override any such generalities.

Good luck!