I actually like Wakka. He's not the brightest bulb in the box, but he's dependable, he's got good people skills, he's a goodhearted and ordinary guy. Very down-to-earth. It's a much-needed contrast to some of the more glamorous and flashy figures in the party.
I actually haven't really got much problem with someone marrying the older brother of someone she loved. It happens. And I can see that however much she might complain that he was no Chappu, in fact, brothers do tend to resemble each other somewhat, so she might eventually start seeing in Wakka some of the same things that attracted her to Chappu -- once, that is, Lulu came to know Wakka for himself, not just as an imperfect version of Chappu. She and he had been friends and worked together a long time, and they remind me a bit of Spock and Bones, always fighting, but gradually coming to respect each other. I could see that bond transforming itself over time from friends-love to romantic love.
I've noticed how many people find the brother-of-her-dead-lover angle startling, however.
There's the added problem that Lulu and Wakka were apparently raised together somewhat like big brother and sister to Yuna, so their relationship is slightly familial. But honestly, that's the way it is in small villages.They are almost incestous.
I have two basic problems with Lulu/Wakka.
They're not compatible. Lulu scares him. He drives her nuts. I have seen relationships that are the Odd Couple, but gosh, they are odd! She is glamorous (the msot well-dressed person in Spira, as far as I can tell) and remote and works with magic. He's a down-to-earth, ordinary guy, who's a jock. It's like a witch and a muggle. They really don't fit, to me.
But the most serious reason is that I trust Lu at her word. Tidus egged her towards Wakka a few times. Her response was not the least bit warm. Finally she told Tidus that he had a lot to learn about women and that "getting along" was not enough, not by a long shot. Possibly the lady doth protest too much?
But I don't think so. I really, profoundly, hate women being protrayed as fickle and wishy-washy. She SAID she wasn't interested, many times. She appears stupid, weak, or clueless, if she then falls in love with him.
I may be a complete hypocrite here, come to think of it, since my story gives Lulu and Auron rather a long time on the pilgrimage before they realize (unfortunately) that they are starting to have feelings for one another. But there, at least, there is a logical progression.