I would like it if the clock didn't start until the moment the player started running. At the beginning of every level, you lose about half a second of precious time waiting to finish spawning. Of course, tighten the medal times to maintain the difficulty level if necessary, but I don't want to have my race times affected by moments in which I am unable to do anything.
As one of the top comments says, the best strategy for surviving 600 seconds is one that involves no power-ups (except possibly the shield power-up, but you shouldn't need that either). When the first giant meteor appears, start firing your normal gun at it until it slows to a near stop. Then, continue to fire at it occasionally, just enough to keep it aloft, while firing on its left or right sides to keep it from drifting too far left or right, respectively. Keep it centered above you. Avoid collecting any turret powerups, as they will sabotage your efforts to keep the meteor on the screen. If you do it right, and have enough patience, 90% of your game time will be spent keeping one giant meteor at bay. I died at 614 seconds, and I would have survived longer if a turret powerup had not spawned literally right at the top of my main turret as I was firing.
The one big flaw that this game shares with all the others of its kind is that there are only so many different things you can build. Ideally, a game where you build the greatest mega-mall in the world would allow you to choose from hundreds and hundreds of stores, booths, and facilities. And, in true Kongregate fashion, most would have to be unlocked through completing milestones.
Protip: If you want to get players excited to play your RPG, give them more than 40 feet of linear dungeon to explore to start with, and don't immediately throw them into a loot quest.
A few tips to help you find your way: To adjust the alignment of orange/purple arrow cells, step up once then down once, or vice versa; for yellow/blue arrow cells, left/right or right/left. For + and - cells, step up or down three times. If no clear path presents itself, move around in the aforementioned ways until it does. When you encounter columns of yellow and blue cells in succession, study their movement and find the one row that lets you step past them in succession, then manipulate the rest of the cells as explained above so that they won't interfere. For some of the levels with X and O cells, you'll have to hit more than one O to reach the end; plan to make one return trip to hit a previously missed O. Study this advice, let it soak into every fiber of your being, and you too can be an Impasse Master.
If someone told me when DSYP came out that the developer of that game was someday going to create a game like this, I would have dismissed it as damned lies. The utter contrast between the two boggles my mind.
It would have been more appropriate for the gems to instead be playing cards. Not only are there 52 of them, but until you collect them all, you're not playing with a full deck.
 "Mr Runner 2"){kind=icon}
 "Reincarnation: The Evil Next Door"){kind=icon}
 "Red"){kind=icon}
 "Shop Empire"){kind=icon}
 "Secretnet"){kind=icon}
 "Murloc RPG: Stranglethorn Fever"){kind=icon}
 "Impasse"){kind=icon}
 "I Wanna Win!"){kind=icon}
 "Another Pointless Flash Button Game Derived From Other Pointless Flash Button Games Inspired For No Absolute Reason Featuring a Random Button That Asks You Random Pointless Objects and Challenges You (Yes you.) To Complete This Super Long Game If You Can"){kind=icon}
 "Bubbles 2"){kind=icon}
 "Villainous"){kind=icon}
 "Whiteboard Tower Defense"){kind=icon}
 "Cardboard Box Assembler"){kind=icon}
 "Skinny"){kind=icon}
 "Kick Out Bieber"){kind=icon}
 "MaXploder"){kind=icon}