Block-pushing puzzle platformer... with a twist! (?)

I chose this genre mostly because I want something simple to work on, and these kinds of puzzle games are generally fun to me. Here's some cropped and artistically positioned alpha screenshottage:



I'll spare you the details of the story and get right down to the mechanics:

-Your character can run and jump and push certain blocks, or other specific objects (for the sake of organization lets call these objects "physics objects").

-Unlike most other block-pushing puzzle platformers, these physics objects can rotate, gain momentum, bounce and crash into walls and other physics objects. The idea is that, though you should be able to get through all the levels by planning-out your course of actions strategically, sometimes a bit of recklessness can pay off in unforeseen ways. Also, it's fun to watch things crash into each other. 

-Physics objects have different weights and properties. There may be blocks that are too heavy to be pushed, exploding blocks, blocks that bounce extra high, etc.

-There are platforms that hold physics objects, but not the player.

-There are platforms that, conversely, hold the player but not physics objects.

-There will be a restart button in case you mess up, which, given how physics objects can be unpredictable at times, it's assumed you will, quite a bit. Levels will be kept fairly small for this reason.

Most of the levels will be "get from point A to point B" type objectives, but it might be fun to throw in additional challenges like "destroy the bridge" or something like that. I haven't decided yet if having enemies in the game would add or detract from the game, but for now, there are none.
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Some initial concerns:

-Since the puzzles are more free-form than traditional games of this genre, it'll take a lot of playtesting to make sure that the levels are possible and/or not too easy.

-I am, so far, completely inept at building custom behaviors, and have even been having trouble with some preexisting ones (specifically "one way platform"). I'm hoping that will change...
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So. Feedback. Brainstorms. Help. I'll take it all. Thank you.

For restart thing, I think you could make bigger levels if you make checkpoint system. Then game will be restarted from the last one intead of from beginning. Good examples of flash games with good checkpoint system are VVVVVVVVV and I believe Amil.

Sounds like a good idea. Either way, the plan is to keep the puzzles from being too spatially expansive. I don't know how I feel about making puzzles that require multiple screen widths to solve. It's looking like that's something I'll have to do eventually, but for the first few levels, it doesn't seem fair to have puzzles that you could screw up before you're even able to see the whole thing.

I love the idea! The way the blocks explode and crash and bounce reminds me of Boom Blox... Still, one question:
If there are blocks that are too heavy to push, why don't you just make them anchors?