I played through all 3 GU games, and my opinion at the end was kind of "wow, I just spent (I can't remember, 45? 60?) hours playing those games..." and I kind of regretting spending that long on a vidya.
It's important to point out, however, that the GU series is one of three rpgs that I managed to play to completion on my ps2. I quit playing most.
I watched the anime prior to playing the game, skimming parts that dragged.
There are also undub versions around, so you can listen to Suzaku and Saber's voices.