For a first time reel I think you show some potential. In general though everything is quite evenly spaced which results in some slow and floaty animation. Animation is all about contrast, you should try and have a variety of speeds of motion to add interest to your work.
Creature walk: Nice and smooth but a bit weightless. Watch some reference of quadrupeds walking, you will notice that they have to straighten and lock their legs as they carry their weight. Bent legs give the illusion of a very light creature, try straightening them on the passing positions.
Waiting boy: The timing for all his actions is roughly the same. It would be more interesting if when he looked round at the start he appeared to hear something, which makes him whip his head around faster. He could then have more of a reaction when he realises that whoever he is waiting for has not arrived. This would bring some contrast to the shot, and also serve to make him feel more alive. As we often say on this blog, reference would help a lot here to give you ideas and help with your timing.
This is how Blue Sky animator Jeff Gabor uses reference for his character work. Watch and learn.
Older man: Again, this is very light. The man appears to float across the room, find some reference of a man in his 60's and watch how he walks. Try and add some character to the man's actions too, we as a viewer don't know what he is thinking. Why is he in this room? Is he scared? Is he looking for something? Is someone looking for him? Is he allowed to be there? Make sure you know why you are animating before you start.
Girl walk cycle: This is better as it has less of a floaty feeling. Make sure you get a proper foot roll as the feet leave the ground, and that they overlap through the passing position. Right now they leave the ground with a 'click' and remain at the same angle when moving forward.
See this for more info: http://www.11secondclub.com/helpful_hints/put_it_there
Moom opening hatch: This has the right ingredients but has a very 'pose to pose' feeling. Try breaking things up by overlapping the head and chest a bit in your breakdown poses. Again, reference will help you bring more interest to the shot. If you had reference I think you would see that your feet wouldn't stay locked to the ground as they do in your shot, and that the performance of pulling the door would be more interesting. This is a fine exercise, but always try and bring something of yourself into the work. He might readjust his position to try and get a better hold on the door for example.
Thanks for submitting, keep going with it!