MLookerCL is a video player based on QuickTime and CoreImage. It allows you to open all the video and audio formats that QuickTime can open and it presents a rather different graphical user interface that feels cumbersome and very well designed. If you have Perian installed, MLookerCL will be able to open pretty much any video format, even those not supported by QuickTime.
My problems with MLookerCL started the second after I ran it for the first time. After trying to load an HD H.264 file, the application hanged for about 10 seconds. It then came back to life and started playing the file in full-screen. I wasn't able to find a way to decrease the size of the video. I tried with the escape key, the Cmd+F combination, and even double clicking on the video, but nothing worked. I also went to the menus on the menubar to no avail. Whenever you click on the video, it will be paused, and the dock will appear on top of the video, that can be a little frustrating.
Once the video started playing, the performance of this application was good. It worked with subtitles and played the video and audio smoothly and in sync.
Another problem I experienced was that to advance or go back during a video, I had to go to the menu and enable the control bar. This is not convenient at all.
In short, I don't see any features that would make me use this application over plain-old QuickTime. The developer's website doesn't even list the feature list.