Dawn of War: Soulstorm. The game itself is fine, I enjoy the other DoW games too, but the loading times..... oh god the loading times. THAT is BORING.
RuneScape. I played it a while when I was much younger. I was only interested in the tradeskills, not the fighting, but eventually I got tired of repeatedly clicking rocks to get ores, hiking halfway to Mongolia to smelt them and then hiking back to smith and sell them. And the combat itself? Most boring combat I've ever seen outside of the sloth wrestling subculture.
Earth 2160. The game is fun, I'll give it that, and well-made (apart from the voice acting..... but let's not open that can of twelve-feet-long eye-devouring hellworms of doom again), but the defences are horrendously powerful and the only "artillery" you have for most of the campaign consists generally of anti-tank rockets, so destroying defences takes FOREVER. And then you have to kill the base behind it. Oh goody goody.