*Once things got going, it was never dull and quite entertaining. From when the Foot Clan invades the Turtles' lair onward it's a blast. The fight scenes are really well-done and fun to watch. The fight choreography is vastly better than the 1990 version.
*There are a lot of good callbacks later in the movie to stuff that happens earlier, like the "don't move no matter what" in the climax. And good callbacks to the animated series, including Shredder's vow to eat turtle soup, Vernon making a reference to "heroes on a half-shell," etc.
*I liked the back-story between Sacks and the Shredder.
*Megan Fox did a pretty good job playing April O'Neill. I liked Judith Hoag in the 1990 version better, but it wasn't a bad performance. A lot of people don't think she's a talented actress and I really haven't seen that many of her movies, but she does seem to play a particular type of character (spunky young female with a chip on her shoulder?) well enough. And I did like the character--they combine her different back stories (in some versions she's a scientist or daughter of a scientist, while in others she's a newspaper reporter) in a coherent way.
*A lot of people thought the Turtles' new designs were nightmarish or creepy, I'm guessing due to the Uncanny Valley effect. They didn't bother me. I actually thought they were kind of cool. And Splinter using his long tail as a fifth limb for fights--such as his epic throw-down with the Shredder--was awesome.
*They bring in Karai, although her relationship with the Shredder (in many versions she's his daughter, adopted daughter, granddaughter, etc) is never really explained beyond the fact she gets to explain herself and not get mashed when things go wrong.
*It had a lot of funny moments.
*The early part of the movie kind of drags. Things pick up after the Foot Clan takes hostages in the subway and the Turtles proceed to take the perpetrators apart, but the slow beginning isn't helpful.
*The Shredder's master plan is really kind of dubious. I could understand how [NAME REDACTED TO AVOID SPOILERS] would benefit from his part of it--the Foot Clan could have simply been providing muscle in exchange for part of the eventual profits. That'll go into the "how I would've done it" post I wrote tonight.
*There's a pivotal scene I would have done rather differently, but going into detail would be spoilery. It was all right, but it could've been much better. That'll go into the "how I would have done it" post as well.
*The Shredder is too bulky. I would have preferred him more lithe like he was as a powered-armor-free ninja in most of his incarnations. Given how gigantic and steroidal the Turtles are in this incarnation some kind of enhancement was necessary to make him a realistic threat, but something more akin to Iron Man would've been better.
It's not the greatest movie ever, but it's not bad either. Worth seeing once. 7 out of 10.