Celli

Yeah, Sen's is one of those "Oh boy, let's get this over with" areas for me. The only things I dislike about Blighttown is those stupid Toxic Blowdart fuckers that thankfully don't respawn after you kill them, and the unbearable lag if you dare play this game on console. Otherwise, Blighttown is probably one of the better areas in the game imo.

Addendum: But nothing compares to the asinine design of Lost Izalith. Before you ask, it's basically an unfinished area that you're forced to go to towards the end of the game. Terrible level design paired with a terrible boss at the end. This is why I dislike the 2nd half of DS1.

I had very little trouble with Blighttown, but Sen's Fortress was just a frustrating mess of garbage. Blighttown can at least be taken in a careful manner, but the fortress, nope. 

@Kyoshi I must have died at the last trap so many times because you have to sprint across as the right time. At least the boss isn't too bad. And it leads to the best area in the game.

@Redeye Funnily enough I didn't mind lost Izalith. The bed of bullshit is the worst though.