Twixtor is probably the best. It's not as simple as just slowing down the shot. There are dozens of different combinations of settings that vary depending on the shot. It also takes a bit of experimentation to do really good slow mo from a normal shot. It would help me a bunch if you could describe the kinds of things you're trying to do. It would help even more if you had some example footage.
The other thing to keep in mind, is the frame rate that the footage was shot at VS the playback rate you are setting up. Twixtor is so far the best that I know of (admittedly, I have not got the world of experience with all the plug-ins available), and is "pretty" simple to get going.
For best results, I have found - shoot at a high frame rate, set a comp to play it back at 50% speed (so shoot at 50FPS, and playback at 25FPS for me), export the result as lossless PNG or TGA files, then use those along with twixor to slow it down even more.
I see the two slow mo shots. In the first there's a little something funny going on for a couple of frames with dhe door frame. Otherwise it looks just fine I'm not a fan of game screen cap videos and I'm not a gamer so I don't know what you are looking for but with the right settings and setting up some control and vector masking areas Twixtor is very capable of fixing the problems with the door frame. I didn't see any problems with the slow mo at the end and I only noticed the few frames of distortion in the door frame after watching the section about 4 or 5 times. If you could post the frame where the distortion is giving you a problem at the end of this clip I'll make a guess as to how to fix it but my answer will probably be the same. Go through the advanced Twixtor tutorials on their site and learn how to protect those areas in your shot. BTW, because screen cap games are different animals than live video and screen cap software produces different kinds of files than video cameras do you may have other issues with the footage that cannot be solved easily.
One other question, and please don't take this as a criticism or an insult. Why are you spending your valuable time creating a slow mo sequence of game play? I'm just curious.
Search Google for Advanced Twixtor Tutorials
Check out the tutorials, especially the Edge and fixing warping ones on the company website.
Read articles like this one where users explain their techniques.
Ok I will definitely check out their tutorials thanks for your help and the reason I want to do the slow mo is so I can make a gameplay montage which is something that alot of people do for this game here are a couple examples http://www.youtube.com/watch?v=rLy1rvNJTXg http://www.youtube.com/watch?v=BeXIB4cmKSQ