Okay, so a summary of what I thought about the game's content:
Areas I liked:
Firelink Shrine
Undead Burg/Parish
Darkroot Garden/Basin
Kiln of the First Flame (really great ending area with some excellent environmental storytelling)
New Londo Ruins
Anor Londo (probably the best area in the game)
The Duke's Archives
The Painted World of Ariamis
Oolacile (all DLC areas)
Areas I didn't like:
Lost Izalith - just awful. My least favourite part of the game. Rubbish enemies, dull design and annoying constant damage from the lava
Crystal Cave - a neat idea, but poorly paced, walkways you can fall off by no fault of your own and irritating invisible walkways
Sen's Fortress - I kind of like the idea of this trap-filled area but I didn't like the execution all that much and found it very cheap
Tomb of the Giants - again, a good idea but I didn't like the execution much, and I really disliked the crawling skeletons/dog skeletons, who are too strong and have annoying flail attacks
Blighttown - I liked the idea and it was probably the most draining area in the game, but the technical performance is soooo bad that it really affected my enjoyment
Bosses I liked:
Ornstein & Smough (hard as hell, but very enjoyable)
Great Grey Wolf Sif
Knight Artorias
Sanctuary Guardian
Chaos Witch Quelaag
Iron Golem
Gwyn, Lord of Cinder
Dark Sun Gwyndolin
Bosses I didn't like:
Bed of Chaos
Demon Centipede
Demon Firesage
Ceaseless Discharge
Hydra (I don't think the game copes well with larger bosses and this was cheap as you're right on the water's edge)
I didn't defeat Manus and Kalameet from the DLC, and the Hydra in Ash Lake, and the others whom I haven't mentioned I don't particularly have an opinion on or am ambivalent towards.