You must be joking. FFVIII is hardly underrated, judging by all the fanboys/fangirls who go raving on about it. There are even some which I can probably guess on Eyes on FF. There's probably a decent amount of fanboys/fangirls of FFVIII more than there are haters. It's a highly overrated game, though probably not as overrated as FFX and definitely not as overrated as FFVII.

There was no "depth" to FFVIII more than any other love story. Maybe there was more "depth" than the love stories of other FF's, since all of FFVIII was about Rinoa and Squall's love. As to the R=U theory, didn't Rinoa only get sorceress abilities because Ultimecia possessed her? That's probably why she only got "Angel Wing" after when she was possessed. As for Griever, she probably only created him out of Squall's imagination, probably to scare him. And if R=U were true, why would Ultimecia be fighting Rinoa? Without going into Time Compression jargon, Rinoa was Ultimecia before turning evil right? Well, that would mean that if Rinoa was dead, Ultimecia wouldn't exist then. Like people say, there really is not enough proof for R=U other than theories and "symbolism" in the game. And symbolism can be determined in many ways.