Alright, I've seen a couple of threads revolving around the Nazi Zombies mini-game and I like some of the ideas they mention, but I have to HEAVILY disagree with many of the weapon choices some say are best.
For starters, never, EVER pick the Flamethrower or Panzerschrek. These two put your entire team at major risk as you get up in the levels.
I'm proud to say that using the following tactics, myself and my roommate (2 people) managed to make it to level 17 before being destroyed (for 2+ players; though done with just 2):
1: Start off in the main room (duh). For the first couple of rounds, expire all of your pistol ammunition. This will net you a plethora of points to spend later on. The minute you can, purchase the Carbine rifle.
2: If you've been a good aim, you should have more than enough to enter room 2 ("HELP!" Door). Do this around level 3. Above anything, do NOT move the couch in Room 1 (Starting Room). This will screw you over in the later rounds.
3: Stick around in the second room. This room will be your haven for the next couple of levels. Here, you have a random gun generator (RGG) and a double barreled shotgun. Take it. Then, use the RGG. The gun you want is the Ray Gun. It has a 160 capacity, with 20 round clips, and moderate reload speed. Another extremely important factor is the splash damage, which can kill zombies with one hit every time. So the Ray Gun should remain your secondary weapon from this point on. Also, you should attempt to obtain the STG44, FG (either of both types), or the MG for one of your troops. Otherwise, just stick with the Double Barreled Shotgun or attempt to pick up the Sawed-off Shotgun from the RGG.
4: In early levels, you will have slower zombies. Save at least ONE zombie for the purpose of closing up all barricades. He will run around after you, while you close them up, or restock ammunition. Since he's slow, it will take him a while to get to you, giving you ample time to do your business. By doing this, you also give yourself more time in the next level. Once you're done, kill him. This can also be done with two people and a faster zombie by leading him around barricades while someone else cleans up. This will become impossible later on, unless you have enough dedicated "bait" to accomplish this. Never attempt with more than one remaining Zombie.
5: From rounds 3 - 7, you should run from Room 2 to Room 1 and be sure to clean up as much as possible. If need be, have one troop cover Room 2 while the other covers Room 1. Adjust according to number of players. Watch each others' back constantly. These rooms are small and it's easy to be overwhelmed here.
6: Now it's time to open the next room. In Room 2, there is a second staircase (the first being the verboten one in Room 1) which leads to Room 3A (Upstairs). Open this and head on up. You should be able to do this around Level 7. Pick up the Trench Gun here if you haven't been using the Sawed-off Shotgun, which is also accessible upstairs in Room 3B (The Subroom). To get to Room 3B, go up the stairs, past the clock, and hang a left.
7: In Room 3A you have a slight choke point (staircase to Room 2) and Five windows (Room 3). Another important point to note, is that Room 3B has only one window, one doorway (second room chokepoint) and a staircase leading to Room 1. Now you see why you shouldn't open this staircase. Here's where you will start making your stand.
8: Because Room 3B has only two viable entrypoints, you have the ability to funnel zombies in through either the doorway, or the window. Having the Ray Gun and Trench Gun/Sawed-off Shotgun will aid you UNENDINGLY here. The Sawed-off is now available and is near the doorway chokepoint. With two people, the second person should have a machine gun that ISN'T the Browning, MP40, BAR, or Thompson. The STG44, FG (both versions), and MG are all amazing weapons with heavy stopping power, large clips, and good capacity. The FG and MG are decent weapons, but due to their high Rate Of Fire (ROF), they're not the best choice. Remember, if you're relying on RGG weapons, you will also be relying on getting a Max Ammo pickup. This could bite you in the butt. Hence, the reason to have one troop use the Trench Gun or Sawed-off Shotgun. Take into account any recoil and adjust accordingly for each gun.
8: Be sure to watch the window as well as the doorway. Let any in, and you're done for.
Use this guide to keep the game going. Also, don't be afraid to use grenades to slow down Zombies.
Primary: Trench Gun, Sawed-off Shotgun, FG, Deployable FG, MG
Secondary: Ray Gun
good tips thanks
Close your eyes, open up ya mouth, and count to ten,
Don't wanna, huh? Cuz ya know my nuts are goin' in,~ICP
[This message was deleted at the request of the original poster]
-To reach Room 3B, head up the stairs and IMMEDIATELY to the left. The room is a slight blue/purple-ish colour.
-Second Point 8 should be Point 9.
-Also, between rounds after Round 7, be sure to restock on any available ammunition.
-Use Insta-Kill to full advantage and don't be afraid to knife if you have to.
-Keep the window in Room 3B covered and closed at all times.
-Head shots do the most damage, and earn you the most points, but are harder to get and totally wasteful in later rounds. Stick to chest/body shots.
-Watch for crawling zombies. Don't miss them, or they will get you when you least expect it.
P.S. Using these tactics, my roommate has made it to Round 11+ on his own. It's possible to utilize these on solo.
Other Liner Notes:
-Since this strategy is based on luck, it won't ALWAYS work. Just remember that the Ray Gun is your best bet for survival. Most of this game runs on luck as it is, so most "guides" will be based on gambles, as well as proper team co-ordination.
-The Thompson is useful in early rounds, but useless later on
-The MG is the best when it comes to later rounds due to it's high capacity clip and ROF. Have at least ONE MG gunner in your group
-Sawed-off Shotgun kills almost instantly. UTILIZE THIS.
-The Flamethrower still sucks. No matter what. Unless crossed with Insta-Kill. Even then, you're outnumbered and risking it.
-One last time: GET THE RAY GUN!
-You will want to marry Max Ammo and Insta-Kill. Trust me.