having played FF7 many times and looked at his exact scenes though? No, he was sincere in his speech
Apparently playing the game many times doesn't keep you from completely misinterpreting a scene many times.
I assume you're talking about the scene where he promises to rule the world with fear, and it's a lie. Seriously, look how popular he is later in the game (visit Junon, Kalm in particular). Either you view that as inconsistent writing, or of signs of him being a manipulator, and the latter view is supported by the tabs he keeps on your party (Cait Sith, obviously) throughout the game.
(If, incidentally, you're talking about a different speech, then ignore this rant.)
Final Fantasy 7:
President Shinra: 5/10. Y'know what? While he did need more screentime badly, I have to give him at least an average score just for that scene where he watches the destruction of Sector 7 with classical music playing in the background. The guy had style.
Rufus: 8/10. Yeah, I like Rufus a lot. LOL TINY BRONCO aside, he comes accross as exceedingly competent, and a ruler ready to do what is needed to clean up the mess of Sephiroth and solidify his own empire. And I did like the scenes when he expresses his disgust at Heidegger; it seems he doesn't have absolute power and can't get rid of the guy like he'd want to.
Heidigger: 6/10. Memorable scumbag.
Scarlet: 3/10. Kinda tosses away her character worth in that slapping scene.
Sephiroth: 7/10. Eh, sure. The North Crater scenes are very effective. Suffers from the worst effects of FF7's writing and translation otherwise, but... good enough. When in doubt, go with Tonfa. Actually I'll largely be doing that the rest of the way, so...
Reno: 8/10. Is awesome.
Rude: 5/10. Plays off Reno well.
Elena: 5/10. Yep.
Jenova: Bleh. I dunno if this is a DNR or not, I'll think about it.
Tseng: 6/10.
Hojo: 3/10. I really didn't like how they tried to ninja him into this big important role suddenly at the end of Disc 2. Didn't think it worked well, and Hojo himself lacks the charisma needed for said role.
Palmer: 5/10.
Don Corneo: I hate Don Corneo more than 95% of RPG villains, but Tonfa is right. Mmm, abstain.
Final Fantasy 8:
Edea: 6/10. Had stage presence.
Ultimecia: 2/10. Didn't, really.
Seifer: Only has character worth if he's taken in an ironic fashion. I'm not sure if he should be or not? Though we did name the Seifer clause after him, yes. Eh, 5/10.
Fujin: 6/10. Above average for that scene where she drops her gimmick voice, was effective.
Raijin: 5/10.
Adel: 1/10. No.
Final Fantasy 9:
Kuja: 9/10. Rant time! First of all, I hated Kuja for two discs (HI, I'M POWERFUL AND ARROGANT), but that doesn't matter since that's not what his character is about, it's all setup. It is about, yes, him being "emo". Except he isn't whining about how his life is pain, but a simple, believable fear of death, one of the most basic, primal motivations out there. This is why his arrogance is needed for his character; when he goes from believeing he is going to rule the world for all eternity to realising that no, he's about to die, it is completely crushing, and coupled with his greatly inflated view of himself, leads him to his logical conclusion that yes, it wouldn't be fair for others to exist without him. Very compelling, chillingly believable (given the implausible basic story of a person created to be a powerful living weapon), and had me buying in like few villains before or since.
Brahne: 3/10. ARROGANT AND ... okay, not so powerful ultimately. Last scene with Garnet may save her juuust a little, I dunno.
Thorn/Zorn: 2/10. They have awesome music.
Necron: 1/10. Zeromus is BACK.
Lani: 3/10. Uh huh.
Beatrix: 6/10. Had style, as a villain. (This score is a rating of her up until mid Disc 2.)
Garland: 6/10. Is named Garland, at least.