• Vastly different art style. A lot more seedy and colourful as opposed to the older games' more gothic look.
• Think there's pretty much only a single puzzle in the entire game, whereas puzzles where surprisingly prominent in the older ones.
• No lock-on.
• No Styles system, although a lot of those abilities were incorporated into Dante's general moveset.

I think a lot of what it comes down to is the combat that really turned people away, like the lack of a lock-on, enemies that restrict you to using a particular weapon rather than allowing you to consistently mix it up however you want, it being significantly easier to score S ranks, and the boss battles, while they look flashy, are mediocre compared to the stuff found in DMC3 & 4. That, and DmC's unlockable weapons pale against the creativity and personality of the stuff you found in the older games.

I say all this as someone that still enjoyed my time with DmC, though, and think it made a lot of improvements pertaining to the aesthetic, soundtrack, story, and Dante in particular was a huge improvement over the nigh-unbearable DMC4 Dante. But I still vastly prefer the core gameplay in DMC3 & 4 overall. There's a sense of impact in DMC4 especially that I found a little lacking in DmC. Playing as Nero is perhaps the most fun I've had across the whole series.

What was Wrong with Dante in the fourth installment?

@theacidskull: If you're talking about the newest DmC Devil May Cry..yah, you really should it's awesome..