Say what you want about George RR Martin killing off main characters right and left, but he does seem to save the particularly grisly deaths for the real baddies. Remember Daenery's brother's horrible death-by-molten-gold poured on his head? Joffrey's painful death by poisoning at his nuptials pales in comparison yet was entirely satisfying. "Red Wedding," part deux indeed.
I always knew Joffrey wasn't long for this world, not only because he was a horrid little elfin sadist, but because the actor who played him, Jack Gleeson, has been quite vocal that once his time on the show ended he would give up acting. This is probably a good idea because, though he was delightfully wicked, there was always something a little off about his acting; I felt like I was watching a high school production of King Lear or something.
Poor Tyrion is blamed for the death, though we know it was really Joffrey's fool that carried it out. Now he will be banished to a cell somewhere until he can either prove his innocence or wait for the Lannisters to lose their power. He had already sent his mistress packing after fearing that she would be killed, now that his loving family had found out about her.
The whole scene of him dumping her was like a boy in an old Disney movie who has to banish his beloved hound dog 'cause Pa wants to shoot him. "You go on, now, git!" cries little Jimmy, choking back tears. "I never loved you! You're a mangy mutt! Now go!" Tyrion tells her that she's a whore and has probably banged half of Winterfell and a few White Walkers and direwolves even, all the while being ripped apart inside, we infer.
The best scene however came when Joffrey lay dead in his bitchy mother's arms and she looks up at the skies, cursing the forces that decided to take away her beloved. "As Gods as my witness..." she seems to say. There will be hell to pay, indeed. Since I haven't read the books I have no idea what manner of destruction will come, but since she is a Principal Baddie, I'm sure she'll get revenge somehow but then die by being skinned alive by a wraith and eaten. I'll get the popcorn.