Awsome!
Its so amazing, here are a few hints to get the best worm, here are some upgrades that helped me alot (not in order of getting them)
1. Fat tail
2. Big teeth
3. Fat tissue
4. Small wings (i tried big wings, they were cool but lagged my system which has windows seven and good RAM to hell)
5. Smooth skin
6. Outward spikes
Also heres some other random tips:
1. Black bombs do more damage then mines (about 0.343434% more)
2. Yor worm can get so big he doesnt fit underground (try to avoid this or else bombs always hit you)
3. Speed can help you jump higher
4. Mechs do more damage than futuristic tanks
5. Future helicopters are the only thing that doesnt appear until sandbox mode
Also remember that when you die you can resume from your last upgrade :)
Hope this helps anyone with trouble