Things you didnt like about 2k3 tmnt
 

I loved the 2k3 tmnt but there are some flaws or peeves that I always hated
The dumbing down of Casey
April becoming a ninja master in a short time
Whenever Leonardo hit someone with his swords they fall back
Fake move techniques like double phoenix punch and dragon kick

Some moments that looked like they needed to be expanded on, but weren't. And also closure for some traumatic situations that were left open ended.

this plus:

Mike's lack of nunchaku skills
Color coded weapons (wtf)
Complete raping of some comic storylines (ex: Sons of the silent age)
Shredder's armor only having blades one one hand

Bishop is annoying (but interesting when fighting Shredder because it's bad guys against bad guys) he's too skilled at fighting.

And Baxter Stockman coming back aaaaall the time, that was annoying too.

It's true that Casey seemed dumb.

No Technodrome.

They didn't show the Shredder Wars from season 7 (the events that led to it).

Darius Dunn's fate.

My only real beef was that Baxter NEVER DIES!!! I mean, c'mon- how could he possibly survive all that abuse and dismemberment, TIME AFTER TIME, and not just die?? It was a little ridiculous.

I was cool with Bishop- at least he had a good reason for sticking around so long. And I would have liked to know what happened to Darius, but since they left so soon after he was caught, it was no big deal. I would have liked to see more of the Dark Turtles' fates, too, but it wasn't necessary.

I always thought the Turtles themselves were a little too bulky. And despite 2k3 being my favorite Turtle Series, to me, it clearly had the worst toy line.

All that talk from Splinter and Karai about the one, TRUE, Shredder returning - for us to see nothing.

The turtles' beefcake designs.

The animation for Fast Forward and Back to the Sewers .

I don't like the background music tracks....

Ninja weapons made of wood deflecting laser beams.

And Raph and Leo can craft swords from junk in a farm.

April and Casey quietly disappeared from the Turtles' adventures the longer the series ran. Ironically, ever since they became a couple.

I love 2k3 but if there is one thing that I wish happened is that the second FF season was made instead of BTTS, but maybe the last 2 episodes could have occurred in the "present" and the wedding gone on as per BTTS.

The overly bulky designs for the turtles (their muscles look like balloons, it's almost as bad looking as DBZ's overly butch style).

The many, many, many animation goofs and inconsistencies.

Casey being a complete moron, who seemed to get worse as the show went on.

April's super ninja skills after such little time training (this also applies to Archie's April, 2007 Movie's April, and Nick's April as well-but at least Nick's April had her butt appropriately handed to her when she faced off against a ninja who's been training their entire life).

Too much of the storylines were focused on Leonardo.

Mikey's horrible negative character development (or should I say character regression) as the show went on.

Hun (seriously, all he does is scream at his opponent to let them know he's about to charge at them...and then get his butt kicked embarrassingly easily. He got a teeny bit more interesting when he became Karai's rival, but it wasn't much of an improvement IMO)

The Notes From The Underground storylines and the Garbageman/Nano episodes.

Fast Forward (at least I was able to sit through Back To The Sewers)

Leo getting stabbed by Karai, and then he impossibly manages to wiggle out of his sheath as he passes out so it remains stabbed on her blade as she stares at it all horrified/stunned (I know it was for dramatic effect, but really? This falls under the animation goofs/inconsistencies I mentioned earlier, but because it bothered me so much I just had to list it).

The really awful voice acting during dramatic moments (especially Splinter).

The octagon-shaped bruises.

The various cop-outs following dramatic moments ("Oh no, so and so's injured! Oh, wait, nevermind they're totally fine. Sorry false alarm! Let's make a lame joke to wrap this moment up now...")

The guys (and their weapons) getting anime-inspired-power ups during The Lost Season. I'm not against the guys having chi/energy powers, but it was just so poorly executed in the show.

There's more, but these were the first to pop into my head...

I almost forgot about the "too much Leo" part!!! hahaha, yeah, the show might as well have been called "Leonardo and Bros". He was SEVERELY overpowered.

And Mikey's increasing annoyingness over the years.

Mikey's character regression was a BIG problem for me. I totally hated it.

All of Fast Forward. I could barely sit through it.

Splinter being stuck in cyberspace throughout most of BTTS and Serling being stuck with the Turtles. Ugh.

Oh my gosh it was terrible!

The character designs.
The melodrama.
How it's painfully unfunny.
Mikey.
Reused fight animations.

the series isnt supposed to be funny

Yes it was, don't kid yourself. That was the point of all those awful jokes. It even had its own comedic punchline noise type thing.