After a little under 4 hours of recorded play, with 17 deaths:
Level # ..... Time Score .. Damage Score .. Diamond Score .. Enemy Score .. Total
01 ............ 3800 ......... 40000 .......... 10000 ............ 0 ...... 53800
02 ............ 2700 ......... 40000 .......... 10000 ............ 0 ...... 52700
03 ............ 3400 ......... 40000 .......... 10000 ............ 0 ...... 53400
04 ............ 1600 ......... 40000 .......... 10000 ............ 0 ...... 51600
05 ............ 2600 ......... 40000 .......... 10000 ............ 0 ...... 52600
06 ............ 4600 ......... 20000 .......... 10000 ........ 16000 ...... 50600
07 ............. 200 ......... 40000 .......... 10000 ......... 7000 ...... 57200
08 ............ 2200 ......... 40000 .......... 10000 ........ 14000 ...... 66200
09 ............ 5400 ......... 36400 .......... 10000 ............ 0 ...... 51800
10 ............ 3500 ......... 16400 .......... 10000 ............ 0 ...... 29900
11 ............ 5400 ......... 20000 .......... 10000 ............ 0 ...... 35400
12 ............ 1400 ......... 40000 .......... 10000 ......... 5000 ...... 56400
13 ............ 1900 ......... 24800 .......... 10000 ........ 10000 ...... 46700
14 ............. 300 ......... 32400 .......... 10000 ........ 12000 ...... 54700
15 ............. 700 ......... 40000 .......... 10000 ........ 14000 ...... 64700
16 ............ 1500 ......... 34800 .......... 10000 ......... 8000 ...... 54300
17 ............ 1800 ......... 40000 .......... 10000 ............ 0 ...... 51800
18 ............. 100 ......... 32400 .......... 10000 ......... 8000 ...... 50500
19 ............ 2100 ......... 40000 .......... 10000 ........ 15000 ...... 67100
20 ............... 0 .......... 1800 .......... 10000 ........ 10000 ...... 21800
So, 19 gold medals and 1 silver (which apparently puts me at the top of Grip Games' leaderboard, across both their games). I don't think I can get a gold on the last level. You basically have to keep restarting it until the random item placement puts 1 or 2 health packs near the beginning, and then you have to try to power through and survive with just enough life that you can make the return trip without stopping for dangers. That 0 time score I have for the level in Normal difficulty really did come from finishing that run with somewhere between 0 and 2 seconds to spare.
The 0 enemy score levels are ones where you can't kill anyone. Levels 6, 10, and 11 have no health packs, so the best you can do in them in Hard mode is half health (i.e., 20,000 for damage score). Level 19 is the one I'm most proud of; there is exactly enough ammo to take out all the enemies, so you can't miss if you want to get all of them, and you have to execute your boss attack very precisely and only get hit a few times if you want to be able to finish the stage with a full health 40,000 damage score.
Anyone get a gold on Level 20?