It's simply not very fun.
Well... it looks good, I can give you that much...
But aside from the rather good artwork, there's really nothing that sets this game apart from many, many others like it- and it's just so damned BORING.
You are supposedly saving some of your friends and leaving others, but nothing in the game reflects this. I've been asked to rescue the same person twice or three times in the same game. I've been asked to rescue people I explicitly left behind in an earlier stage, again, often several times. Is there even a point to this mechanic? It doesn't seem to affect the game AT ALL, no matter who I choose to save. All it seems to notably change is the portrait and name of the person I'm supposedly rescuing, despite not seeing hide nor hair of anyone that isn't me or an enemy at any point during the stages themselves.
The enemies are boring as hell, too. I'll give you the possibility that you MIGHT have added new enemies beyond the fourth stage (which, I'm sorry, but four stages is all I could take of this game) that had AI patterns that were not "move toward you and deal contact damage", but everything I saw acted the exact same way, give or take minor speed adjustments or an HP buff in the case of the larger zombies. The original Robotron, the very first game of this type, had enemies that acted in distinct ways- why can't this game? What's more, the regenerating health you give the player works so well that unless you stumble into about 50 or 60 zombies at once, you can just immediately walk off anything that comes your way- there is really no point to trying to avoid most damage. The bosses aren't much better, most of them having only one attack that's typically extremely easy to avoid, only serving to annoy the player by being complete damage sponges of the highest order. Remember how I said I couldn't take more than four stages of this game? The battle with Frankenstein's monster, with his metric assload of health and enemies CONSTANTLY swarming the battle area, took so damn long- not because it was in any way difficult, but because it was a tedious pain in the ass to zigzag around to avoid damage from the legions of zombies while TRYING to land a hit on the boss- was the kicker that made me decide that this was not a game worth finishing.
And the weapons... Not only are there only five of them, INCLUDING your default gun, the four 'special' weapons are mostly either useless (How am I supposed to hit anything going faster than a dead stop with the Teddy Bomb?), aren't really any better than your default weapon, or require so much upgrading to MAKE useful (In terms of both general power, AND the complete ammo starvation you give us on the specials until upgrades) that the player is likely to be bored with the game before they even bother to try obtaining and using the upgrades, especially since the upgrades cost so damn much.
Really... this just isn't a good game. There are plenty of other games that play just like this but are far better at what they do. Decent graphics and a shitload of movie quotes alone do not a fun time provide.