I actually quite liked Tidus, he was a well balanced consistant character, unlike Cloud who changes so quickly. At firts he's like "I don't care about the planet" and then he's all like "We gotta save the planet!" And this is all in the first third of disc 1. At least Squall took some time to change and grow as a character.

Tidus is a naive optimistic charcter, which he should be because he is fairly young and he doesn't know much about Spira, which is understandable. People don't like Tidus because he isn't as dark as Cloud and Squall, which he doesn't need to be. And I suppose out of all FF protagonists, the player sees Tidus's most inner thoughts the most, which will either make you love him or hate him.

But the reason why I like Tidus (and Zidane) so much is that the makers didn't try too hard to make him cool, unlike cloud and squall. Tidus is just a typical impulsive young man who hass so many feelings, not a hardened battle veteran who thinks they're too cool for school.