Attempting to watch it now. Can you elaborate on why you didn't like it compared to the anime? I haven't seen the original material ever.
All spoilers are in white text!
Ok here goes, this will be a very long post so my apologies if it's TL;DR.
First things first, while yes, I understand that the director attempted to fast forward the plot of the anime to ensure that the "meat" could fit into an hour and fourty minutes... this simply cannot be done with an anime like Death Note. I'm sorry, this is nothing more than a circus movie thinly veiled to gauge American interest in one of the all-time great animes. This movie sold itself short by removing the purist American audience and attempting to appease the hipsters and emotional teenagers of the United States. Pathetic at best, and quite frankly, infuriating.
What made (IMO) the anime so good was the evolution of a character from a sincerely interested pro-social "savior" to a power hungry pseudo "God" whose own ego buries him. The plot of L vs. Light is so deeply vetted in genius and logic, all while made apparent to even the dumbest observer. Liken it to Sherlock Holmes vs. Moriarty. It isn't just two genuises pitting their intellects against each other. It's much more, it's personal. Such a plot requires time to play out, to allow for the twists and turns of the serve and return. It's through this process of intellectual combat that you endear yourself to the side of L or Light. Because after watching the anime you will quickly ask yourself: "What really is justice?".
The movie doesn't engage the audience even in the slightest regarding this fact. The very poor (near Twilight levels) of romance between "Mia" (who is Misa in the anime) and Light is nothing more than a distraction.
To this point:
In the anime, Light isn't coached through his decisions by Misa. If anything, it is the other way around.
Look no further than SPOILER:
How Light "coaches" (more like manipulation) Rem and Misa through L's suspicion of Light while both Misa and L are locked away under 24HR surveillance.
The love story is overdone, as in the anime SPOILER:
Light says himself that he will USE Misa's adoration for him as a means to further his own twisted identity of being a savior. There is very little love given from Light to Misa at any point during the Anime. It's all a manipulation.
On to what I think of L.
This absolutely pissed me off. ALOT is assumed of what he knows about Light. You are left thinking "ok, this guy is a genius... so I'll just believe what he says". The amount of time provided in the anime to simply experience L (and Light's) deductive reasoning skills is (IMO) very entertaining.
In the movie, you see see him make rather large sweeping assumptions, such as:
1) Light is in Seattle, based on the fact that a criminal was killed whose identity was only shown on Seattle TV networks? Very weak logic.
2) Light is Kira, simply because he didn't kill his Dad? Also very weak logic.
In the anime L uses many tests to confirm his supsicions of Light SPOILER:
Putting a criminal on TV to pose as L, to see if Kira can kill with only a face and name.
Observing the times of killings, which he deduces to after school hours (due to light being a student)
L releasing criminal identities in batches across the world to observe spikes in Kira killings leading to a possible regional location.
Placing cameras in Lights house to observe his behaviors after school - which reveals the infamous "potato chip" scene.
You'll just have to watch the anime to see how much better they could've done with L. And the whole ending with him supposedly writing Light's name into the Death Note page? GTFO with that BS.
Here's a HUGE SPOLIER:
LIGHT USES REM - MISA'S SHINIGAMI (DEATH GOD) - TO KILL L AND WATARI!!!!!!!!!!!!!!!!!!!!!!
YEP, MISA HAS HER OWN DEATH NOTE AND SHINIGAMI IN THE ANIME!
Ugh there is just so much more I hated.
And again, before anyone says "they cant fit this all into a movie", then my response will be DON'T MAKE THE MOVIE!
Near isn't even mentioned, Mia should've been able to see Ryuk after touching the death note, and the whole Light's Mom being dead sub plot completely distracted from the ego-maniacal motivation seen from Light in the anime.
I have to get to bed, but if you have any more questions feel free to ask ^.^!