Concerning Tidus' apparent 'annoying, whiny' persona: if you were cast off into a world you didn't know or understand, I would imagine you would whine too -- I certainly would. Your world, as you know it, is gone. That's a really startling issue to deal with. I thought his character got this point across nicely. Concerning the laughing scene, it's certainly awkward… but I think it does a decent job conveying how Yuna and Tidus are developing a bond at that point in the story.
As for the comparison to FFXIII, unlike X, I didn't believe the acting in XIII -- the emotion felt phoned in on most occasions (except for Vanille and Fang), or it was way too over the top (see the fireworks scene with Snow and Serah (spelling?) ). I found X's acting and emotional content truly genuine, and remains my favorite of the FF's I've played