I loved the Pharos personally... though the basement levels are not exactly fun but at least they are optional. If you are level 50ish, you are pretty much at the point the rest of the storyline dungeons and boss fights won't be an issue. You'll simply need levels now for the higher tier Mark Hunts. My personal favorite is still Man of Mystery... Best optional boss battle ever... at least for an FF.

Now that you have passed Giruvegan, you should go back and fight Ultima. Easily the hardest of the Esper battles (well Zodiark as well but he's a cheating bastard) not to mention going after Chaos in Nabudis.