Devil May Cry 2, for just about everything. There was some attempt to take the series further in the horror direction (agonized faces in the walls of the first level were a nice touch), but the utterly terrible job done on EVERYTHING else (camera, combat, voice acting, enemy design, level design, etc. etc. etc.) just screwed it up.
I am personally of the camp that enjoyed and supports every iteration of the series after this, though God, DMC4 could have been so much better if they just gave us one more thing: more STORY. When you have a main character clearly willing to give his life and hurl himself headlong into fuck-me odds for the sake of a love interest, you at least TELL US SOMETHING about the love interest! Or the main character! Or the love interest's older brother who has what could have been a heart-wrenching final scene, instead of just slapping scant details into an instruction booklet and going "Yeah, we totally spent every dime and minute we had updating the graphics like morons when the game had to be on two systems, one of which is inherently inferior graphics-wise ANYWAY, and didn't get past the outline stage for the plot".
...for crying out loud they made a stale archetype like VERGIL in DMC3 interesting and deep with only a few specific lines, yet the only hint of that writing ability you see in 4 is from Nero after the first Agnus fight. And the lines are connected to Vergil!
And, if I can step away from my own fan rantings for a moment, Jericho. I said this in an earlier thread, but it bears repeating. Halfway through the game, Barker remembered he was a horror writer. Suddenly you actually start to give a shit about the characters and their plight: even the really annoying ones. And this continues, right up until a dramatic second-to-last act when the reality of the whole thing comes crashing home, and you get all geared up for one climactic final battle...
...And then we get to the final battle. And just damn it. Evidently Barker suffered a stroke at EXACTLY THE MOMENT HE HAD TO WRITE OUT HOW THE LAST BATTLE WENT. The two best characters die, and the whole thing is nothing more than a glorified quicktime event that serves only to highlight that the murder of the people you'd finally come to care about only occurred because they couldn't be worked in, mechanics-wise. And then there IS NO ENDING.
Ugh. Damnit Barker.