The last 21 seasons of The Simpsons have pretty much been unwatchable. Seasons 3-8 and a few episodes of Season 9 are comedy perfection, then with Season 10 the show went downhill and continued to go downhill and went into "Wow so they've completely given up" territory. The writing staffs have been horrible and the producers are just milking whatever nostalgia people have for the show that's still left. I'll stick to watching the old episodes and don't care about any new properties the show has to offer.
Even Season 10 has some fab episodes. One of my absolute favourites is from there:
Like most of the thread has mentioned already though, I have zero faith in the team that has been running the show for the last 20 years.
EDIT: Went back to check, there are even more great episodes than I remember in 10. Lard of the Dance, The Wizard of Evergreen Terrace, Treehouse of Horror IX, When You Dish Upon a Star, Lisa Gets an 'A', Mayored to the Mob, Viva Ned Flanders, Wild Barts Can't Be Broken, Sunday Cruddy Sunday, Homer to the Max, I'm with Cupid, Make Room for Lisa, Simpsons Bible Stories, Mom and Pop Art and Monty Can't Buy Me Love.
15/23 ain't so bad.
Season 13 is where I think the show plummets.