Actually, the animation was pretty good, but very slow.

Generally, if you imagine yourself to be walking around or turning around or sitting down or leaning backwards and back (or whatever), think not only of what movements are made, but also how long it takes to do them. Granted, you're working with minifigs and they're not humans, but things seem much more natural when they move in a "familiar" way, so to speak.

There's two things you can do here: either animate with a higher framerate, or change your animation style so that it includes less frames. Because pretty much everything was too slow and the animation was generally smooth, I'd go with shooting with a higher framerate (I'm guessing you used something like 5FPS or 8FPS here?) like 12 or 15FPS.

There was one point where the animation itself was not very good. When the guy was sitting down and standing up, that movement was too fast. Remember that just because the studs aren't keeping the minifig in the right position, you should just skip some frames. Use supports behind him (out of screen) to have him "half sitting down"; this will work much better.

Ahh, that's where it went wrong then. Yes, unless you're planning to do it all like the old animation studios and shoot at 24FPS with doubles, you might want to put Image Hold to 1. Pretty important because it's bound to mess up your frame rate when you export it.

At this moment it's comicy when it comes to the pacing, yes. Perhaps 12fps would be a better speed for you; inserting more frames in your walk cycle could help too.